Osteochondrosis dissecans der Hüfte beim Erwachsenen - Differenzialdiagnostik freier Gelenkkörper - Fallbeschreibung

Supraacetabular fossa (pseudodefect of acetabular cartilage): frequency at MR arthrography and comparison of findings at MR arthrography and arthroscopy

PURPOSE

To evaluate the frequency of the supraacetabular fossa (SAF) (pseudodefect of acetabular cartilage) at magnetic resonance (MR) arthrography of the hip and to compare the MR findings with those from arthroscopy.

MATERIALS AND METHODS

All patients gave written permission for anonymized use of their medical data for scientific purposes before the imaging examination. The study was submitted to the institutional review board, and the need to obtain additional approval was waived. A medical student, a radiology fellow, and two senior radiologists reviewed 1002 consecutive MR arthrograms for the presence of an accessory bony fossa in the roof of the acetabulum, or SAF. SAF was classified into two types: type 1, which was filled with contrast material on MR arthrograms, and type 2, which was filled with cartilage. The width of the SAF was measured on coronal and sagittal MR images. MR arthrograms showing SAF were evaluated for subchondral reactions. Findings at MR arthrography were compared with those from arthroscopy in four hip joints with SAF type 1 and 13 with SAF type 2.

RESULTS

Sixteen of the 1002 hip joints (1.6%; four female and 12 male patients; mean age, 20.1 years) had SAF type 1 (mean width, 5.2 × 4.5 mm). Eighty-nine hip joints (8.9%; 43 female and 46 male patients; mean age, 37.8 years) had SAF type 2 (mean width, 5.1 × 4.7 mm). No subchondral changes were found around the SAF. No cartilage defect was seen at the site of the SAF at arthroscopy.

CONCLUSION

The high frequency of SAF on MR arthrograms (10.5%), the absence of subchondral reaction, and the absence of cartilage defects at arthroscopy indicate that the SAF of the acetabulum likely represents a variant.

Osteochondritis dissecans of the femoral head

Seven patients with symptomatic osteochondritic lesions of the femoral head are presented. All were male with a mean age of 26 years (16 - 33 years). Two distinct morphologic appearances of the hip joint could be identified. Five patients presented with a coxa valga deformity, four of whom had signs of epiphyseal dysplasia. There were 2 patients whose hips appeared normal apart from the osteochondrontic lesions. In both cases an additional acetabular rim lesion due to a reproducible femoro-acetabular impingement was diagnosed at arthrotomy. This may have acted as the underlying cause of osteochondritis dissecans in these cases. All 7 patients underwent surgical treatment. An intertrochanteric osteotomy (I.O.) alone was performed in 2 patients. Follow-up of these patients at 6.5 and 8.5 years after surgery revealed that the osteochondritic lesions had not healed and one individual remained symptomatic. In the remaining 5 patients, treatment consisted of femoral head dislocation and screw fixation of the osteochondritic lesion. This was combined with an I.O. in two of these patients for coxa valga and osteoplasty of a broad femoral neck in 2 other patients. All lesions had healed at an average follow-up of 4.3 years (2 - 8.5 years). Three patients were asymptomatic and 2 patients had minor residual pain. No progressive osteoarthritic changes or signs of avascular necrosis of the femoral head were observed.

Osteochondritis dissecans (OCD), an endoplasmic reticulum storage disease?: a morphological and molecular study of OCD fragments

Osteochondritis dissecans (OCD) fragments, cartilage and blood from four patients were used for morphological and molecular analysis. Controls included articular cartilage and blood samples from healthy individuals. Light microscopy and transmission electron microscopy (TEM) showed abnormalities in chondrocytes and extracellular matrix of cartilage from OCD patients. Abnormal type II collagen heterofibrils in "bundles" and chondrocytes with abnormal accumulation of matrix proteins in distended rough endoplasmic reticulum were typical findings. Further, Von Kossa staining and TEM showed empty lacunae close to mineralized "islands" in the cartilage and hypertrophic chondrocytes containing accumulated matrix proteins. Immunostaining revealed: (1) that types I, II, VI and X collagens and aggrecans were deposited intracellulary and (2) co-localization within the islands of types I, II, X collagens and aggrecan indicating that hypertrophic chondrocytes express a phenotype of bone cells during endochondral ossification. Types I, VI and X collagens were also present across the entire dissecates suggesting that chondrocytes were dedifferentiated. DNA sequencings were non-conclusive, only single nucleotide polymorphism was found within the COL2A1 gene for one patient. We suggest that OCD lesions are caused by an alteration in chondrocyte matrix synthesis causing an endoplasmic reticulum storage disease phenotype, which disturbs or abrupts endochondral ossification.

Fluoroscopically based drilling of the femoral head in a model of adiposis

OBJECTIVE

Exact drilling into the ischemic areas of necrotic lesions of the femoral head remains a challenging procedure, particularly in obese patients. This study was conducted to evaluate the precision of fluoroscopically based drilling and the associated radiation exposure in an in-vitro model of adiposis.

MATERIALS AND METHODS

In an in-vitro model of necrotic lesions in adiposis, 20 sawbones were drilled under the guidance of an intraoperative navigation system (VectorVision, BrainLAB, Munich, Germany) and 20 more were drilled conventionally under fluoroscopic control only.

RESULTS

A statistically significant difference was found with respect to the distance from the drill tip to the desired mid-point of the lesion, with a mean distance of 0.56 mm for the navigated group and 1.15 mm for the control group. Furthermore, a significant difference was found in the number of drilling corrections required, as well as the radiation exposure time: The navigated group required a mean of 0.35 second drillings or corrections of the drilling direction, compared to 2.45 for the control group, and the duration of radiation exposure was less than 1 second for the navigated group and 3.85 seconds for the control group.

CONCLUSIONS

Drilling guided by the VectorVision navigation system shows high precision, even under difficult circumstances such as those encountered in adiposis, with a marked reduction in the duration of radiation exposure.