A statistical shape model of trochlear dysplasia of the knee.

BACKGROUND: Trochlear dysplasia is known as the primary predisposing factor for patellar dislocation. Current methods to describe trochlear dysplasia are mainly qualitative or based on a limited number of discrete measurements. The purpose of this study is to apply statistical shape analysis to take the full geometrical complexity of trochlear dysplasia into account. METHODS: Statistical shape analysis was applied to 20 normal and 20 trochlear dysplastic distal femur models, including the cartilage. RESULTS: This study showed that the trochlea was anteriorized, proximalized and lateralized and that the mediolateral width and the notch width were decreased in the trochlear dysplastic femur compared to the normal femur. The first three principal components of the trochlear dysplastic femurs, accounting for 79.7% of the total variation, were size, sulcus angle and notch width. Automated classification of the trochlear dysplastic and normal femora achieved a sensitivity of 85% and a specificity of 95%. CONCLUSIONS: This study shows that shape analysis is an outstanding method to visualise the location and magnitude of shape abnormalities. Improvement of automated classification and subtyping within the trochlear dysplastic group are expected when larger training sets are used. CLINICAL RELEVANCE: Classification of trochlear dysplasia, especially borderline cases may be facilitated by automated classification. Furthermore, the identification of a decreased notch width in association with an increased sulcus angle can also contribute to the diagnosis of trochlear dysplasia.

Imageless versus image-based registration in navigated arthroscopy of the hip: a cadaver-based assessment.

The aim of this study was to determine the accuracy of registration and the precision of the resection volume in navigated hip arthroscopy for cam-type femoroacetabular impingement, using imageless and image-based registration. A virtual cam lesion was defined in 12 paired cadaver hips and randomly assigned to either imageless or image-based (three-dimensional (3D) fluoroscopy) navigated arthroscopic head-neck osteochondroplasty. The accuracy of patient-image registration for both protocols was evaluated and post-operative imaging was performed to evaluate the accuracy of the surgical resection. We found that the estimated accuracy of imageless registration in the arthroscopic setting was poor, with a mean error of 5.6 mm (standard deviation (sd) 4.08; 95% confidence interval (CI) 4.14 to 7.19). Because of the significant mismatch between the actual position of the probe during surgery and the position of that probe as displayed on the navigation platform screen, navigated femoral osteochondroplasty was physically impossible. The estimated accuracy of image-based registration by means of 3D fluoroscopy had a mean error of 0.8 mm (sd 0.51; 95% CI 0.56 to 0.94). In terms of the volume of bony resection, a mean of 17% (sd 11; -6% to 28%) more bone was resected than with the virtual plan (p = 0.02). The resection was a mean of 1 mm deeper (sd 0.7; -0.3 to 1.6) larger than on the original virtual plan (p = 0.02). In conclusion, given the limited femoral surface that can be reached and digitised during arthroscopy of the hip, imageless registration is inaccurate and does not allow for reliable surgical navigation. However, image-based registration does acceptably allow for guided femoral osteochondroplasty in the arthroscopic management of femoroacetabular impingement.

Extra-articular hip endoscopy: A review of the literature.

The aim of this review is to evaluate the current available literature evidencing on peri-articular hip endoscopy (the third compartment). A comprehensive approach has been set on reports dealing with endoscopic surgery for recalcitrant trochanteric bursitis, snapping hip (or coxa-saltans; external and internal), gluteus medius and minimus tears and endoscopy (or arthroscopy) after total hip arthroplasty. This information can be used to trigger further research, innovation and education in extra-articular hip endoscopy.

A custom-made guide for femoral component positioning in hip resurfacing arthroplasty: development and validation study.

In the field of hip resurfacing arthroplasty, accurate femoral component placement is important to achieving a positive outcome and implant survival in both the short and long term. In this study, femoral component placement was defined preoperatively using virtual computed tomography-based surgical simulation of a classical posterior surgical approach. Custom-made surgical drill guides were produced to reproduce the surgical plan in the operating room. We first developed a custom-made guide for guide-wire placement to position the femoral resurfacing component. Then, to assess the accuracy in vivo, the custom-made guide was evaluated in five patients with normal anatomy. The first hypothesis of this patient study was that the use of custom-made neck guides would allow for an average accuracy within the range of ± 4° for the drill path and ± 4 mm for the entry point of the guide-wire. A second hypothesis was that three-dimensional preoperative planning would enable the prediction of an implant size differing by a maximum of one size from the size eventually implanted. The presented hip resurfacing guide performed well in terms of fit, stability and accuracy. The in vivo accuracy study revealed an accuracy of 4.05 ± 1.84° for the drill path and 2.73 ± 1.97 mm for the entry point of the guide-wire. The predicted component sizes and the implanted component sizes differed maximally by one size, confirming our hypothesis. We conclude that these preliminary data are promising, but require further validation in a full clinical setting in larger patient groups.

Hip arthroscopy in patients with painful hip following resurfacing arthroplasty.

PURPOSE: Determining the etiology of persistent groin pain after hip resurfacing arthroplasty (HRA) can be very challenging, even for the experienced surgeon. The purpose of the present study was to evaluate the use of hip arthroscopy as a diagnostic and therapeutic tool for the painful hip following resurfacing arthroplasty. METHODS: In the present paper, the indications for arthroscopy and the arthroscopic findings in 15 patients with persistent and incapacitating groin pain following HRA are described. In all patients, nonsurgical diagnostic investigations such as ultrasound and radiography, blood sample analysis, and technetium and leukocyte-labeled scanning were inconclusive so that a definite diagnosis could not be established. RESULTS: In seven patients, synovial biopsies were taken arthroscopically to rule out metal sensitivity, low-grade infection, or excessive metal wear. A definite diagnosis from histological evaluation could be made in 5 out of the 7 patients. Five patients were clinical suspicious of iliopsoas tendinitis. Diagnostic arthroscopy and histological analysis of the synovial samples provided an alternative diagnosis in 2 out of the 5 patients. Three patients underwent femoral osteoplasty for impingement due to reduced anterior femoral offset with subsequent symptom relief. CONCLUSION: Hip arthroscopy after HRA is a valuable diagnostic alternative to open procedures in case of persistent groin pain, when noninvasive investigations fail to explain the symptoms. Multiple tissue samples should always be taken for histological examination and culture, as they are crucial in the final identification of the origin of the complaints.

A method for three-dimensional evaluation and computer aided treatment of femoroacetabular impingement.

Several theoretical models have shown that the range of motion of the hip joint is impaired in patients with femoroacetabular impingement, and that the acetabular cartilage is at risk of being damaged as a result of abnormal shear stresses, even during normal everyday activities. Computer aided technologies might add to the early diagnosis and adequate treatment of such lesions. This paper describes the technique, theories and algorithms we have developed for patient-specific detection, analysis and computer aided surgery of femoroacetabular impingement. Currently available models applicable to femoroacetabular impingement offer modeling based on collision analysis of a constrained hip joint. Such an approach implies that neither the femur nor the acetabulum can be analyzed completely separately for the presence of structural lesions responsible for the impingement problem. Moreover, a constrained model does not allow for comprehensive prediction of the possible locations and extent of secondary cartilage lesions (so-called contre-coup lesions) of the posterior acetabulum opposite the anterior impingement site. We report a new technique for the subject-specific morphological analysis of the proximal femur, acetabulum and hip joint. The technique offers a number of advantages compared to currently used techniques for the diagnosis and evaluation of hip impingement, and has direct orthopaedic applications as it allows computer aided planning and minimally invasive surgery for patients with femoroacetabular impingement.

Correlation between inclination of the acetabular component and metal ion levels in metal-on-metal hip resurfacing replacement.

We examined the relationships between the serum levels of chromium and cobalt ions and the inclination angle of the acetabular component and the level of activity in 214 patients implanted with a metal-on-metal resurfacing hip replacement. Each patient had a single resurfacing and no other metal in their body. All serum measurements were performed at a minimum of one year after operation. The inclination of the acetabular component was considered to be steep if the abduction angle was greater than 55 degrees. There were significantly higher levels of metal ions in patients with steeply-inclined components (p = 0.002 for chromium, p = 0.003 for cobalt), but no correlation was found between the level of activity and the concentration of metal ions. A highly significant (p < 0.001) correlation with the arc of cover was found. Arcs of cover of less than 10 mm were correlated with a greater risk of high concentrations of serum metal ions. The arc of coverage was also related to the design of the component and to size as well as to the abduction angle of the acetabular component. Steeply-inclined acetabular components, with abduction angles greater than 55 degrees, combined with a small size of component are likely to give rise to higher serum levels of cobalt and chromium ions. This is probably due to a greater risk of edge-loading.