[Imaging in joint-preserving hip surgery]. / Bildgebung in der gelenkerhaltenden Hüftchirurgie.

Instability and impingement of the hip are the main pathomechanisms that can lead to chondrolabral damage, painful restriction of motion and early hip osteoarthritis due to increased mechanical stress, even in young patients. The goals of joint-preserving hip surgery are correction of the osseous deformities and chondrolabral damage as well as restoration of joint function. A prerequisite for successful surgery is the identification of the underlying hip pathologies, which can also occur in combination. Dedicated radiographic and magnetic resonance (MR) imaging of osseous morphology and the internal degenerative joint lesions play an essential role for the treatment indications and surgical treatment planning. This article provides a concise overview of the prevalence, pathomechanisms and indicated treatment of hip deformities as well as detailed recommendations on the specific radiological clarification.

Femoral cartilage damage occurs at the zone of femoral head necrosis and can be accurately detected on traction MR arthrography of the hip in patients undergoing joint preserving hip surgery.

The primary purpose was to answer the following question: What is the location and pattern of necrosis and associated chondrolabral lesions and can they be accurately detected on traction MR arthrography compared with intra-operative findings in patients undergoing hip preservation surgery for femoral head necrosis (FHN)? Retrospective, diagnostic case series on 23 patients (23 hips; mean age 29 ± 6 years) with diagnosis of FHN undergoing open/arthroscopic joint preserving surgery for FHN and pre-operative traction MR arthrography of the hip. A MR-compatible device for weight-adapted application of leg traction (15-23 kg) was used and coronal, sagittal and radial images were acquired. Location and pattern of necrosis and chondrolabral lesions was assessed by two readers and compared with intra-operative findings to calculate diagnostic accuracy of traction MR arthrography. On MRI all 23 (100%) hips showed central FHN, most frequently antero-superiorly (22/23, 96%) where a high prevalence of femoral cartilage damage was detected (18/23, 78%), with delamination being the most common (16/23, 70%) damage pattern. Intra-operative inspection showed central femoral head cartilage damage most frequently located antero-superiorly (18/23, 78%) with femoral cartilage delamination being most common (14/23, 61%). Traction MR arthrography enabled detection of femoral cartilage damage with a sensitivity/specificity of 95%/75% for reader 1 and 89%/75% for reader 2. To conclude, femoral cartilage damage occurs at the zone of necrosis and can be accurately detected using traction MR arthrography of the hip which may be helpful for surgical decision making in young patients with FHN.

Patients with severe slipped capital femoral epiphysis treated by the modified Dunn procedure have low rates of avascular necrosis, good outcomes, and little osteoarthritis at long-term follow-up.

AIMS: The modified Dunn procedure has the potential to restore the anatomy in hips with severe slipped capital femoral epiphyses (SCFE). However, there is a risk of developing avascular necrosis of the femoral head (AVN). In this paper, we report on clinical outcome, radiological outcome, AVN rate and complications, and the cumulative survivorship at long-term follow-up in patients undergoing the modified Dunn procedure for severe SCFE. PATIENTS AND METHODS: We performed a retrospective analysis involving 46 hips in 46 patients treated with a modified Dunn procedure for severe SCFE (slip angle > 60°) between 1999 and 2016. At nine-year-follow-up, 40 hips were available for clinical and radiological examination. Mean preoperative age was 13 years, and 14 hips (30%) presented with unstable slips. Mean preoperative slip angle was 64°. Kaplan-Meier survivorship was calculated. RESULTS: At the latest follow-up, the mean Merle d'Aubigné and Postel score was 17 points (14 to 18), mean modified Harris Hip Score was 94 points (66 to 100), and mean Hip Disability and Osteoarthritis Outcome Score was 91 points (67 to 100). Postoperative slip angle was 7° (1° to 16°). One hip (2%) had progression of osteoarthritis (OA). Two hips (5%) developed AVN of the femoral head and required further surgery. Three other hips (7%) underwent implant revision due to screw breakage or change of wires. Cumulative survivorship was 86% at ten-year follow-up. CONCLUSION: The modified Dunn procedure for severe SCFE resulted in a low rate of AVN, low risk of progression to OA, and high functional scores at long-term follow-up. The slip deformities were mainly corrected but secondary impingement deformities can develop in some hips and may require further surgical treatment. Cite this article: Bone Joint J 2019;101-B:403-414.

Proof of concept: hip joint damage occurs at the zone of femoroacetabular impingement (FAI) in an experimental FAI sheep model.

OBJECTIVE: In ovine hips chondrolabral damage as seen in cam-type femoroacetabular impingement (FAI) can be induced via an intertrochanteric varus osteotomy. However, it is yet to proven whether the observed cartilage damage is caused by a dynamic cam type impingement. Thus we asked, (1) whether actual cartilage damage observed after FAI induction in ovine hips occurs at the predicted, computed zone of FAI; (2) whether the extent of cartilage damage increases with ambulation time in this animal model? DESIGN: In this experimental, controlled, comparative study 20 sheep underwent unilateral FAI induction through an intertrochanteric varus osteotomy. Preoperatively sheep underwent computed tomography to generate three-dimensional models of the osseous pelvis and femur. The models were used to predict impingement zones before and after simulated varus osteotomy using range of motion (ROM) analysis. Sheep were sacrificed after 14-40 weeks of ambulation. At sacrifice cartilage was inspected and (1) location of actual damage and computed impingement zones were compared; (2) Cartilage damage was compared between short- and long ambulation groups. RESULTS: (1) The average location and the extent of peripheral and central cartilage lesions did not differ with the computed impingement zones (all P > 0.05). (2) Grades of central, posterior cartilage damage were more severe in the long-compared to the short ambulation group (2.2 ± 1.8 vs 0.4 ± 0.5; P = 0.030). CONCLUSIONS: In this experimental ovine FAI model the surgical induction of an osseous impingement conflict between the femur and acetabulum causes cartilage damage at the zone of simulated FAI.

Usefulness of MR Arthrography of the Hip with and without leg Traction in Detection of Intra-articular Bodies.

RATIONALE AND OBJECTIVE: Although intra-articular bodies are a classic indication for MR arthrography and surgical removal, diagnostic studies are currently sparse. To assess the diagnostic performance of MR arthrography with and without leg traction in detection of intra-articular bodies in the hip joint. MATERIAL AND METHODS: The institutional hip arthroscopy data base (2009-2016: 631 hips) was retrospectively reviewed. Inclusion criteria were hips with and without intra-articular bodies and direct MR arthrography performed with and without leg traction. Twenty-one hips with intra-articular bodies constituted the "disease-positive" group. Seventy-nine randomly selected hips without intra-articular bodies constituted the "disease-negative" group. Images were reviewed independently for presence of intra-articular bodies by two blinded readers. Overall diagnosis and location of intra-articular bodies was recorded (peripheral or central). Arthroscopy served as goldstandard for diagnosis and location of intra-articular bodies. Diagnostic performance and kappa statistics of traction MR arthrography with and without traction were calculated. RESULTS: For both readers sensitivity/specificity of traction MR arthrography was 86%-95% respectively 90%-91% for overall diagnosis of intra-articular bodies and was 81%-86% respectively 90%-92%for MR arthrogrpahy without traction. For central intra-articular bodies sensitivity was higher for both readers with traction (79%-89%) than without traction (74% each). CONCLUSION: MR arthrography with and without traction of the hip is highly accurate in identifying central and peripheral intra-articular bodies. Application of traction was further useful for visualization of centrally located intra-articular bodies.

Femoral osteochondroplasty can be performed effectively without the risk of avascular necrosis or femoral neck fractures in an experimental ovine FAI model.

OBJECTIVE: The experimental induction of cam-type femoroacetabular impingement (FAI) in sheep is established. To tap the full potential of this ovine model, one should be able to perform a femoral osteochondroplasty safely. This study was based on previous cadaver experiments on the blood supply to the ovine femoral head and on the biomechanical strength of the proximal femur following offset creation. We hypothesized that offset creation in this ovine FAI model does not lead to (1) avascular necrosis (AVN) of the ovine femoral head or (2) iatrogenic femoral neck fractures and (3) can be performed effectively. DESIGN: In this experimental, controlled, prospective study nine sheep underwent unilateral FAI induction through an intertrochanteric, varus osteotomy. Seventy days following FAI induction, femoral osteochondroplasty was performed. Sheep were sacrificed after another 140 days. Radiographs, computed tomography (CT) scans and MRI were acquired. Histologic samples were stained with hematoxylin-eosin. (1) The multimodal Association Research Circulation Osseous (ARCO) classification was used for assessment of AVN. (2) Femoral neck fractures were assessed with the multimodal imaging approach. (3) Pre- and postoperative (=after sacrifice) alpha angles and femoral neck diameters were compared. RESULTS: (1) No signs for AVN according to the ARCO classification or (2) for femoral neck fractures were detected. (3) Mean alpha angles and femoral neck diameters decreased significantly (p < 0.001) superiorly by at least 30° respectively 4 mm after the offset creation. CONCLUSIONS: Femoral osteochondroplasty can be performed effectively and without the risk of AVN or femoral neck fractures in this ovine FAI model.

The modified Dunn procedure for slipped capital femoral epiphysis: the Bernese experience.

PURPOSE: Based on previous investigations on the vascular blood supply to the femoral head, a technique for anatomical reduction after slipped capital femoral epiphysis was developed. This technique is a modification of the original technique by Dunn using a retinacular soft-tissue flap. This allows the visual control of the epiphyseal vascular blood supply. We report the experience at the inventor's institution with a critical discussion of the available literature. METHODS: Using a trochanteric osteotomy for surgical dislocation of the hip, a retinacular soft tissue flap is created containing the deep branch of the medial femoral circumflex artery, the external rotators and the capsule. The femoral epiphysis can be mobilised safely and reduced on the femoral neck after resection of the almost constantly present reactive metaphyseal callus. RESULTS: In our institution, the rate of avascular necrosis with 2% is comparably low to Dunn's original results. It is only present in cases where no bleeding was already evident before reduction of the epiphysis. The ten-year long-term results are favorable in these cases with a good functional result and only little progression of osteoarthritis. However, other authors have reported higher rates of avascular necrosis up to 24% in their initial experience. CONCLUSIONS: In experienced hands using the correct meticulous surgical technique, the results are favorable regarding the rates of avascular necrosis, the functional outcome and the development of radiographic osteoarthritis - even in acute and severe cases. Avascular necrosis is rare but can be observed if there is no evidence of intra-operative femoral head perfusion before and after reduction of the epiphysis.

[Impingement of the hip]. / Impingement der Hüfte.

Femoroacetabular impingement (FAI) describes the repetitive painful contact between the acetabulum, the pelvis and the proximal femur. This bony abutment can lead to a characteristic pattern of chondrolabral damage and is one of the main etiological factors in the development of juvenile osteoarthritis of the hip joint. This article describes the current treatment concepts of FAI and the radiological assessment including an overview of standard measurement methods, coxometric parameters and cut-off values. Furthermore, the authors stress the importance of a profound understanding of the entire configuration of the pelvis and the dynamic interplay of its components.