Acetabular Fossa Research Articles

The shape of acetabular cartilage optimizes hip contact stress distribution

The biomechanical role of the horseshoe geometry of the acetabular cartilage is described using a three-dimensional mathematical model. It is shown that the acetabular fossa contributes to a more uniform articular contact stress distribution and a consequent decrease in the peak contact stress. Based on the results it is suggested that the characteristic horseshoe shape of the articular cartilage in the human acetabulum optimizes the contact stress distribution in the hip joint.

A histological study of articular cartilage after rotational acetabular osteotomy for hip dysplasia

Acetabular dysplasia was produced in 24 immature white rabbits. A rotational acetabular osteotomy was then carried out and radiological and histological studies of the articular cartilage were made. In the hips which did not undergo osteotomy, radiographs at 26 weeks showed that residual subluxation remained and arthritic changes such as narrowing of the joint space or dislocation were still seen. However, in the operated group there was a remarkable increase in cover, but arthritic changes were not observed. After 24 weeks, the Mankin grading score in the operated group was significantly lower than that in the non-operated group. The latter hips showed an irregular surface of the cartilage, exfoliation and proliferation of synovial tissue. In those undergoing osteotomy, primary cloning of chondrocytes or hypercellularity was seen and at 24 weeks after operation and metaplasia of the cartilage in the fibrous tissue was observed in the boundary between the medial area of the acetabulum and the acetabular fossa.

Preclinical and clinical evaluation of the image quality of the Iso C 3D image intensifier in comparison to computer tomography for its use in the pelvic area

Intraoperative three-dimensional visualisation using the Siremobil Iso C 3D (Siemens, Erlangen, Germany) has been approved for use in spine and long bone surgery since its recent clinical launch. Insufficient visualisation quality, seen in obese patients and in cases of low bone density, has somewhat limited its use, however. The first experiences with intraoperative 3D visualisation were attempted using intraoperative CT in the OR, a space consuming technique requiring structural hardware adaptations. Since then, CT scanning within the OR has only been realized in a low number of hospitals, due to the high costs involved and limited hardware mobility. The Siemens mobile C arm (Siremobil Iso C 3D), however, allows acquisition of two-dimensional X-ray images together with the creation of 3D reconstructions. In preparation for clinical use of the Siremobil Iso C 3D in pelvic surgery, the aim of this study was to grade the quality of visualisation in comparison to the gold standard computer tomography in four therapy relevant pelvic regions in 8 human cadavers, including SI screws to exemplify implants in the dorsal pelvic ring. Besides the influence of body mass index (variation from 20.2 to 42.9) and interference of metal artefacts, visualisation quality was evaluated in different pelvic regions. In the regions sacroiliac joint, acetabulum, femoral neck and anterior pelvic ring a score with five subgroups was used, rating the applicability of Siremobil Iso C 3D in pelvic surgery. Visualisation of muscle structures, bony structures and soft tissue was assessed. Grading of image quality in comparable standard projections was performed independently by three surgeons and three radiologists. Each of them rated 12 anatomic structures twice in above-mentioned regions of every cadaver, the subjective best and worst image. Those anatomic structures are sacral foramina, sacral nerve roots, SI joint, intervertebral space L5/S1, osteophyts, muscles, acetabular joint line, acetabular cartilage, subchondral cysts, acetabular fossa, femoral head and os pubis. Average value was calculated for each anatomic region from all assessments of structures. Dependences to region, anatomic structure, BMI and metal artefacts were analysed. Statistic analyses were done by use of Brunner non-parametric analysis of variance and chi-square test. Visualisation quality with metal implant artefacts in dorsal pelvic ring is significantly better in CT. Without metal artefacts statistical significance was only seen in acetabular joint and subchondral cysts, last in dependency to examiner. Visualisation quality of Siremobil Iso C 3D appeared sufficient for both intraoperative and postoperative control in cases with a known preoperative diagnosis. There was no influence of body mass index found in any of the 8 cadavers. Implants positioned in the dorsal pelvic ring reduced visualisation quality, but sufficient estimation of bony structures was still possible. For primary diagnostics, computer tomography remains a clearly superior option due to superior image quality. For intraoperative control of reduction and positioning of implants in pelvic surgery, however, the additional intraoperative use of Siremobil Iso C 3D is considered to offer clear advantages over current two-dimensional C-arm visualisation tools. This is confirmed by first experiences of intraoperative use of Iso C 3D in 11 patients since clinical approval of Siremobil Iso C 3D for pelvic surgery. C11 placement of SI screw by Iso C 3D navigation was done perfectly in two cases after reduction control.

Adhesive capsulitis of the hip (SS-34)

It is postulated that adhesive capsulitis of the hip is more common than suggested by published literature, which recounts only a few isolated cases, and that this condition shares many of the same characteristics seen in the shoulder. The purpose of this study is to report the findings of the first clinical case series on this condition. Methods: Since 1993, all patients undergoing hip arthroscopy have been prospectively assessed. This database currently consists of over 500 consecutive cases. In 1999, adhesive capsulitis was first recognized as a causative factor in patients with recalcitrant hip pain. Since then, 9 patients have been identified with this condition that have achieved at least 1 year follow-up and represent the substance of this report. The indication for arthroscopy was disabling symptoms refractory to conservative treatment with persistent painful restricted motion. Conservative treatment consisted of oral anti-inflammatory medication, lifestyle modifications to avoid offending activities, and supervised physical therapy. The procedure consisted of manipulation under anesthesia and concomitant arthroscopy to assess and address co-existent pathology. Results: There was 100% follow-up at an average of 17.3 months. There were 8 females and 1 male with an average age of 43.7 years. Radiographs were normal in 8 cases and revealed mild degenerative disease in the one male patient. 8 patients had an intra-articular injection of anesthetic which provided temporary relief of their symptoms. Among 7 MRIs, 2 demonstrated an effusion and 1 revealed evidence of an articulolabral lesion. Among 7 MRAs, 2 demonstrated evidence of labral pathology. None of the studies revealed evidence suggesting adhesive capsulitis. Examination under anesthesia revealed restricted rotational motion in all patients with an average loss of 19.4° external rotation and 5.6° internal rotation. Full range of motion was regained with manipulation. Arthroscopy revealed characteristic findings of adhesive capsulitis including hemorrhagic fibrinous debris within the pericapsular recesses and acetabular fossa. Other co-existent intra-articular pathology was present in 6 cases and included 5 articular lesions, 3 labral tears, and 1 partial disruption of the ligamentum teres. The average preoperative score was 53.7 and postoperative 86.7, representing an average improvement of 28 points (range 6–43). There were no complications. Discussion and Conclusions: Adhesive capsulitis of the hip is not as rare as would be suggested by the paucity of available literature. The clinical characteristics are similar to those commonly attributed to this condition in the shoulder, principally consisting of painful restricted motion and a clear predilection for middle aged females. It may occur with or without associated intra-articular pathology. It is likely that many of these may respond to conservative treatment. Recognizing the existence of this process will assist the physician in counseling patients and structuring a conservative recovery program. Arthroscopy can be beneficial in the treatment of recalcitrant cases but may assume less of a role with improved diagnostic skills essential to implementing a proper management strategy.

Adhesive capsulitis of the hip (SS-95)

It is postulated that adhesive capsulitis of the hip is more common than suggested by published literature, which recounts only a few isolated cases, and that this condition shares many of the same characteristics seen in the shoulder. The purpose of this study is to report the findings of the first clinical case series on this condition. Methods: Since 1993, all patients undergoing hip arthroscopy have been prospectively assessed. This database currently consists of over 500 consecutive cases. In 1999, adhesive capsulitis was first recognized as a causative factor in patients with recalcitrant hip pain. Since then, 9 patients have been identified with this condition that have achieved at least 1 year follow-up and represent the substance of this report. The indication for arthroscopy was disabling symptoms refractory to conservative treatment with persistent painful restricted motion. Conservative treatment consisted of oral anti-inflammatory medication, lifestyle modifications to avoid offending activities, and supervised physical therapy. The procedure consisted of manipulation under anesthesia and concomitant arthroscopy to assess and address co-existent pathology. Results: There was 100% follow-up at an average of 17.3 months. There were 8 females and 1 male with an average age of 43.7 years. Radiographs were normal in 8 cases and revealed mild degenerative disease in the one male patient. 8 patients had an intra-articular injection of anesthetic which provided temporary relief of their symptoms. Among 7 MRIs, 2 demonstrated an effusion and 1 revealed evidence of an articulolabral lesion. Among 7 MRAs, 2 demonstrated evidence of labral pathology. None of the studies revealed evidence suggesting adhesive capsulitis. Examination under anesthesia revealed restricted rotational motion in all patients with an average loss of 19.4° external rotation and 5.6° internal rotation. Full range of motion was regained with manipulation. Arthroscopy revealed characteristic findings of adhesive capsulitis including hemorrhagic fibrinous debris within the pericapsular recesses and acetabular fossa. Other co-existent intra-articular pathology was present in 6 cases and included 5 articular lesions, 3 labral tears, and 1 partial disruption of the ligamentum teres. The average preoperative score was 53.7 and postoperative 86.7, representing an average improvement of 28 points (range 6–43). There were no complications. Discussion and Conclusions: Adhesive capsulitis of the hip is not as rare as would be suggested by the paucity of available literature. The clinical characteristics are similar to those commonly attributed to this condition in the shoulder, principally consisting of painful restricted motion and a clear predilection for middle aged females. It may occur with or without associated intra-articular pathology. It is likely that many of these may respond to conservative treatment. Recognizing the existence of this process will assist the physician in counseling patients and structuring a conservative recovery program. Arthroscopy can be beneficial in the treatment of recalcitrant cases but may assume less of a role with improved diagnostic skills essential to implementing a proper management strategy.

Effects of removal of the acetabular labrum in a sheep hip model

Objective: The aim of this study was to learn whether partial resection of the acetabular labrum would lead to degenerative arthritis in an ovine model. Methods: A 2 cm segment of labrum was removed from one hip in 18 mature Swiss Alpine sheep and a sham procedure was performed on the opposite side. Animals were permitted ad lib activity until sacrifice at 6, 12 or 24 weeks. The hip joint was removed en bloc, and loaded with a force of one body weight, using a custom device designed to recreate a physiologic joint reaction force. While under load, the joint was plunge frozen, and then fixed by freeze substitution using aldehydes in methanol/acetone solvents. The entire joint was embedded in methacrylate and sectioned in a standardized frontal plane following the reaction force and including the femoral neck and the acetabular fossa. The sections were evaluated for concentricity and evidence of arthrosis. Six hip joints of three sheep with no surgical procedure were loaded with high or low loads and served as non-surgical controls. Results: Degenerative changes were present in all surgical hips, but the changes were symmetrical and mild. In 16 of 18 hips, the labrum regenerated to the extent that dense fibrous scar extending from the surgically denuded origin filled the defect. Conclusion: Resection of the labrum does not cause rapid degeneration or altered stability of the sheep hip.

Anatomic Assessment of the Acetabular Fossa for Screw Fixation in Acetabular Fracture

Purpose: To obtain spatial information on the acetabular fossa concerning ‘transacetabular screw’ insertion through the acetabular fossa parallel to the quadrilateral surface for fixing an acetabular fracture. Materials and Methods: Each hemipelvis harvested from 25 adult fresh frozen cadavers was sectioned into eight segments. This resulted in seven measuring points located along the outer margin of the acetabular fossa. At these points, we measured and compared the vertical thicknesses of cartilage and bone from the quadrilateral surface. Results: The average thickness of the thinnest portion of the acetabular fossa floor was 3.9±1.9 ㎜. The entire thickness of the bone and cartilage measured vertically from the quadrilateral surface at the 7 points ranged from 12.7±2.1 ㎜ to 17.8±3.8 ㎜. The thinnest safe space of exposed threads of the ‘transacetabular screw’ inserted through the acetabular fossa was consistently just below the posterior conus of the lunate surface, measuring 4.8±1.6 mm (p Conclusion: We suggest that ‘transacetabular screws’ can be inserted safely if due consideration is paid to the spatial characteristics of on the acetabular fossa. Screw insertion into the postero-inferior portion of the acetbular fossa should be done carefully.

Malformation of the acetabular fossa as a cause of intrapelvic injury in total hip arthroplasty: a report of 2 cases

We report 2 cases of bone defects of the acetabulum. The first case was a patient who underwent a total hip arthroplasty. An intraoperative bleeding occurred because of an injury of an intrapelvic artery. Preoperative radiographs did not show this bone defect. A similar abnormality of the acetabulum was found in a series of 30 pelves that were dissected for a cadaver study. In this case, the bone defect was located in the center of the right acetabulum.

Case reports - Free osteochondral fragment caught in the acetabular fossa in the osteochondritis dissecans after Legg-Calvé-Perthes' disease-report of 2 cases

Case reports - Free osteochondral fragment caught in the acetabular fossa in the osteochondritis dissecans after Legg-Calvé-Perthes' disease-report of 2 cases

Effects of traction, distension, and joint position on distraction of the hip joint: An experimental study in cadavers

Purpose: To quantify the effects of traction alone and in combination with distension of air in different joint positions in order to find out the conditions for adequate distraction of the hip joint with minimal traction force. Type of Study: Experimental cadaver study. Methods: Eight cadaver hip joints were studied. The cadavers were placed supine on a fracture table and traction was applied in different joint positions for flexion and abduction with and without distension using air. For the measurement, the joint space between the acetabulum and femoral head was separated by 4 different lines characterizing the lateral margin of the acetabulum, the superior portions of the lunate cartilage, and the acetabular fossa. Results: At all measurement lines, distraction of the hip was significantly better when traction and distension were combined. At traction forces from 250 to 300 N, traction plus distension resulted in a 1.59- to 2.25-fold increase of joint distraction compared to traction alone. The maximum effect of distension was achieved between 200 and 250 N. Up to traction forces of 250 N, the joint vacuum force counted for more than half of the total resistance. The effects of flexion and abduction on distraction of the hip were smaller. A trend for better distraction was found for 20° of flexion and a significantly better distraction by avoiding abduction. Conclusions: High traction forces by breakage of the joint seal can be avoided by distension using air. The passive resistance of the soft tissues increases at higher traction forces. Slight flexion without abduction showed further increase of joint distraction. Reducing the amount of traction may possibly reduce the risk of soft tissue perineal and neurologic injuries.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 8 (October), 2002: pp 865–871

Fate of the osteochondral fragments in osteochondritis dissecans after Legg-Calve-Perthes' disease.

The treatment of osteochondritis dissecans after Legg-Calvé-Perthes' disease has not been clearly determined. It may be either by simple observation or surgical removal of the osteochondral fragment. We studied the evolution of the lesion in 13 children and reviewed 92 hips reported in the literature. In our patients ten showed a tendency towards spontaneous healing, one required drilling + grafting to obtain fusion, and in two there was separation into the joint. These loose bodies were in the acetabular fossa and caused no symptoms. On reviewing the literature, we found only four cases of hips with loose bodies from osteochondritis dissecans. These were lying in the inferomedial capsule and were also asymptomatic. Treatment of osteochondritis dissecans after Legg-Calvé-Perthes' disease should therefore be conservative unless the fragment interferes with the mechanics of the hip.

Fate of the osteochondral fragments in osteochondritis dissecans after Legg-Calvé-Perthes’ disease

The treatment of osteochondritis dissecans after Legg-Calvé-Perthes’disease hasnot been clearly determined. It may be either by simple observation or surgical removal of the osteochondral fragment. We studied the evolution of the lesion in 13 children and reviewed 92 hips reported in the literature. In our patients ten showed a tendency towards spontaneous healing, one required drilling + grafting to obtain fusion, and in two there was separation into the joint. These loose bodies were in the acetabular fossa and caused no symptoms. On reviewing the literature, we found only four cases of hips with loose bodies from osteochondritis dissecans. These were lying in the inferomedial capsule and were also asymptomatic. Treatment of osteochondritis dissecans after Legg-Calvé-Perthes’ disease should therefore be conservative unless the fragment interferes with the mechanics of the hip.

Hip arthroscopy without traction: In vivo anatomy of the peripheral hip joint cavity

Purpose: To describe the in vivo anatomy of the peripheral compartment of the hip joint using a systematic sequence of examination without traction. Type of Study: Case series. Methods: We performed 35 hip arthroscopies without traction from an anterolateral portal in the supine position. Free draping and a good range of movement of the hip joint were used to relax parts of the capsule and increase the intra-articular volume of the area that was inspected. Each procedure was documented on a standard protocol including detailed information on technical features and normal and pathologic intra-articular findings. Results: A comprehensive inspection of the peripheral compartment was obtained from the anterolateral portal. A systematic sequence of examination was developed separating the periphery of the hip joint into 7 areas: anterior neck area, medial neck area, medial head area, anterior head area, lateral head area, lateral neck area, and posterior area. The arthroscopic in vivo anatomy of each area is described. In 3 patients, 1 to 3 loose bodies were removed. In 1 patient with a synovial chondromatosis, 40 chondromas were retrieved. In osteoarthritis, impinging osteophytes were trimmed in 3 cases and partial synovectomy was performed in 10 patients. The following complications were observed: a temporary sensory deficit of the lateral femoral cutaneus nerve in 1 patient, scuffing of the anterior surface of the femoral head in 3 patients, detaching of an osteophyte in 1 patient, and partial tears of the anterior synovial fold in 10 patients. Conclusions: Arthroscopy without traction allows for a complete evaluation of hip anatomy without the loaded articular surfaces, the acetabular fossa, and the ligamentum teres. For a complete overview of both the central and peripheral part of the hip, traction is necessary for the central part.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 9 (November-December), 2001: pp 924–931

Hip arthroscopy in hereditary multiple exostoses: A new perspective of treatment

The cases of 2 children (9 and 11 years old) with hereditary multiple exostoses disease are presented. The lesions were located primarily in the acetabular fossa of the left hip and caused pain and limitation of range of motion. Hip arthroscopy was performed to remove the exostoses without damaging the articular surfaces and the Y cartilage. After the procedure, the pain disappeared and normal range of motion was recovered for both children. Conventional surgery would have required hip dislocation to access these lesions with an increased risk of femoral head necrosis. These cases constitute a new and interesting application of hip arthroscopy.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 9 (November-December), 2001: E40

The acetabular point: a morphological and ontogenetic study.

The acetabular point was analysed by studying human pelvic bones from 326 individuals ranging from newborns to age 97 y. The bones were categorised into 3 groups according to the degree of fusion for the 3 elements of the pelvis: nonfused (59), semifused (5) and fused (262). The acetabular point in immature pelvic bones is clearly represented by the point of the fusion lines for each bony element at the level of the acetabular fossa. In adult pelvic bones the acetabular fossa has an irregular clover-leaf shape, the superior lobe being smaller than the anterior and posterior lobes. Cross-sectional analysis of acetabular morphology suggested that the acetabular point in adult pelvic bones is always represented by the indentation between the superior and the anterior lobes of the acetabular fossa.

Pathomorphologic Characteristics of Posttraumatic Acetabular Dysplasia

The pathomorphology of posttraumatic acetabular dysplasia differs fundamentally from the classic developmental dysplasia of the adolescent. The aim of this report is to qualify and quantify the pathomorphologic characteristics of the posttraumatic acetabular dysplasia and to define the requirements for adequate corrective surgery in this type of dysplasia. Retrospective review of the anteroposterior (AP) radiographs of ten patients with symptomatic posttraumatic acetabular dysplasia. In five cases, false profile views and in five cases computed tomography (CT) scans were also available for investigation. Measurements of distances and angles on radiographs and CT scans were made by pencil and goniometer. On the AP radiographs, posttraumatic acetabular dysplasia shows uniformly deformed true pelvis with an angular deformation of the innominate bone averaging 20 degrees in the region of the acetabular fossa that causes the concavity of the pelvic brim to increase in direction of the involved acetabulum and creates both a lateral and a caudal displacement of the acetabulum, averaging twenty-three millimeters and nine millimeters, respectively. The increased width of the inner wall of the acetabulum, measuring an average of eleven millimeters, makes lateralization of the center of the femoral head reach a mean of forty-three millimeters. The acetabular deformity in all cases shows a pronounced lateral deficiency. Ventral deficiency is moderate. All ten posttraumatic dysplastic acetabuli show marked retroversion averaging 27 degrees. In contrast, the contralateral acetabuli shows a mean anteversion of 23 degrees. The morphology of this kind of acetabular dysplasia is uniform and differs significantly from that seen in classic developmental dysplasia of the hip. For reconstructive surgery of such a hip, the challenge to abolish the lateralization of the hip joint to restore normal body weight lever arm is imperative. Because acetabular retroversion is a reproductive feature of posttraumatic dysplasia, it is important to avoid further reduction of the posterolateral containment of the femoral head and augmentation of the anterior acetabular wall, increasing the risk of anterior impingement.

Vorzugsrichtung der Kollagenfibrillen im sub-chondralen Knochen des Hüft- und Schultergelenks

We hypothesised that--due to bending and tension--there should exist a preferential direction of the collagen fibrils in the subchondral bone of the concave components of the hip and shoulder joint that results from bicentric or eccentric loading, but there should be no preferential direction in the convex joint partners. We therefore examined 25 human hip and 27 shoulder joints, these being decalcified after maceration. To analyse the preferential direction of the collagen fibrils, we used the split line method. The subchondral plate was pierced at regular intervals with needles that had been previously dipped in diluted ink. In the acetabulum, we found a predominantly transverse direction of the split lines in the ventral and dorsal horn of the lunatic surface, and these usually continued through the acetabular fossa. In the ventral part of the acetabular roof, arch-like orientations of the split lines were observed. In the glenoid cavity, a clearly preferential orientation was found in anterior-posterior direction, usually in the middle third of the articular surface. In the femoral and humeral heads, no preferential direction of the split lines was observed in any of the specimens. We interpret the split-line patterns in the acetabulum as an expression of the tensile stress that is encountered during a "spreading open" of the socket upon bicentric (ventral-dorsal) loading in the physiologically incongruous joint. In the glenoid, the relatively weak bony support in the ventral and dorsal part of the articular surface may be responsible for bending and tensile stress, particularly in view of eccentric loading during dynamic activity, and this could explain the observed anterio-posterior split line pattern. The results support the idea that the subchondral bone of concave joint partners encounters tension, leading to a preferential direction of the collagen fibrils. This can be considered as a functional adaptation of the subchondral bone on a microstructural level.

Closed Toggle Pinning for Canine Traumatic Coxofemoral Luxation

SummaryA method of closed implantation of a toggle pin bone anchor and prosthetic ligament was developed for the treatment of traumatic canine coxofemoral luxation. Radiographic and anatomical evaluation of the canine femur and acetabulum were performed in order to develop an imaging and instrumentation technique that would allow closed placement of a toggle pin bone anchor under fluoroscopic guidance, while at the same time minimizing, or eliminating, damage to the articular cartilage. The surgical technique was then performed in 14 canine cadaver coxofemoral joints, followed by gross evaluation of implant placement, and potential cartilage or soft tissue damage. The cervical canal radiographic view of the proximal femur allowed placement of the drill hole through the fovea capitis of the femoral head without damaging the articular cartilage. The acetabular fossa was readily distinguishable from the acetabular articular cartilage on both of the lateral and ventrodorsal radiographic views of the pelvis. The toggle pin apparatus was inserted without damage to the articular cartilage in nine out of the fourteen hips and the bone tunnels were situated within the cancellous bone of the femoral neck in each of the nine specimens evaluated. Complications encountered during the procedure included bending and/or breakage of the guide wire in three hips and damage to the articular cartilage in two hips. The success of technique modifications designed to diminish the incidence of these complications awaits investigation in a clinical trial. Closed toggle pinning for canine traumatic coxofemoral luxation has the potential advantage of achieving rapid stabilization of the coxofemoral joint without damage to the articular cartilage and the need for an open approach to the joint. The clinical application of the technique is reported in one patient.The equipment and methodology for closed implantation of a toggle pin bone anchor and prosthetic ligament was developed for the treatment of traumatic coxofemoral luxation. A cadaver study was performed to assess the viability of the technique. Clinical application in one case is described.

股関節内に発生した類骨骨腫のＭＲＩ診断

Osteoid osteoma is a relatively common bone tumor of benign origin and can be easily diagnosed. However, when intraarticular lesions occur, they may pose a diagnostic challenge. Recently, we experienced a rare case of osteoid osteoma in the hip joint of a fifteen-year-old girl and describe the method of diagnosis and treatment.She complained of right hip pain and restriction of motion without any history of trauma or joint disease. The pain was aggravated by motion and she also had night pain. There was no findings on initial roentgenogram, however, two months later roentgenogram had showed a calcified mass in the acetabular fossa. MR imaging in early phase showed only localizad hypertrophic synovium with slight joint effusion. However, Gadolinium (Gd) enhanced MR imaging revealed a ringed area of low signal intensity around a calcified mass. A bony mass covered with synovium was observed in the acetabular fossa using an arthroscope and the mass was excised. Histopathologically itwas diagnosed as a osteoid osteoma with a nidus.From this study it can be suggested that Gd enhanced MR imaging is useful for the accurate diagnosis of intraarticular Osteoid osteoma.

Arthroscopy in 19 children with Perthes' disease. Pathologic changes of the synovium and the joint surface.

Arthroscopy of the hip joint was performed in 19 children with Legg-Calvé-Perthes' disease. Proliferation of the synovium was pronounced both in the acetabular fossa and over the inner wall of the capsule. Hypervascularity was seen on the acetabular labrum in every stage of the disease. Microscopically, hyperplasia of the synovial lining cells was observed, but inflammatory changes in the synovial tissue were inconspicuous in the early stage of the disease. Although hypertrophy of the endothelial cells of the vessels was seen in the late stage of the disease, it was not distinct in the initial or fragmentation stages. Joint pain improved after irrigation during arthroscopy.