Accurate and robust reconstruction of proximal femur from sparse intraoperative data and dense point distribution model for surgical navigation

Constructing a 3D surface model from sparse-point data is a nontrivial task. Here, we report an accurate and robust approach for reconstructing a surface model of the proximal femur from sparse-point data and a dense-point distribution model (DPDM). The problem is formulated as a three-stage optimal estimation process. The first stage, affine registration, is to iteratively estimate a scale and a rigid transformation between the mean surface model of the DPDM and the sparse input points. The estimation results of the first stage are used to establish point correspondences for the second stage, statistical instantiation, which stably instantiates a surface model from the DPDM using a statistical approach. This surface model is then fed to the third stage, kernel-based deformation, which further refines the surface model. Handling outliers is achieved by consistently employing the least trimmed squares (LTS) approach with a roughly estimated outlier rate in all three stages. If an optimal value of the outlier rate is preferred, we propose a hypothesis testing procedure to automatically estimate it. We present here our validations using four experiments, which include 1 leave-one-out experiment, 2 experiment on evaluating the present approach for handling pathology, 3 experiment on evaluating the present approach for handling outliers, and 4 experiment on reconstructing surface models of seven dry cadaver femurs using clinically relevant data without noise and with noise added. Our validation results demonstrate the robust performance of the present approach in handling outliers, pathology, and noise. An average 95-percentile error of 1.7-2.3 mm was found when the present approach was used to reconstruct surface models of the cadaver femurs from sparse-point data with noise added.

An integrated approach for reconstructing surface models of the proximal femur from sparse input data for surgical navigation

A patient-specific surface model of the proximal femur plays an important role in planning and supporting various computer-assisted surgical procedures including total hip replacement, hip resurfacing, and osteotomy of the proximal femur. The common approach to derive 3D models of the proximal femur is to use imaging techniques such as computed tomography (CT) or magnetic resonance imaging (MRI). However, the high logistic effort, the extra radiation (CT-imaging), and the large quantity of data to be acquired and processed make them less functional. In this paper, we present an integrated approach using a multi-level point distribution model (ML-PDM) to reconstruct a patient-specific model of the proximal femur from intra-operatively available sparse data. Results of experiments performed on dry cadaveric bones using dozens of 3D points are presented, as well as experiments using a limited number of 2D X-ray images, which demonstrate promising accuracy of the present approach.

Non-photorealistic rendering of virtual implant models for computer-assisted fluoroscopy-based surgical procedures

Surgical navigation systems visualize the positions and orientations of surgical instruments and implants as graphical overlays onto a medical image of the operated anatomy on a computer monitor. The orthopaedic surgical navigation systems could be categorized according to the image modalities that are used for the visualization of surgical action. In the so-called CT-based systems or 'surgeon-defined anatomy' based systems, where a 3D volume or surface representation of the operated anatomy could be constructed from the preoperatively acquired tomographic data or through intraoperatively digitized anatomy landmarks, a photorealistic rendering of the surgical action has been identified to greatly improve usability of these navigation systems. However, this may not hold true when the virtual representation of surgical instruments and implants is superimposed onto 2D projection images in a fluoroscopy-based navigation system due to the so-called image occlusion problem. Image occlusion occurs when the field of view of the fluoroscopic image is occupied by the virtual representation of surgical implants or instruments. In these situations, the surgeon may miss part of the image details, even if transparency and/or wire-frame rendering is used. In this paper, we propose to use non-photorealistic rendering to overcome this difficulty. Laboratory testing results on foamed plastic bones during various computer-assisted fluoroscopybased surgical procedures including total hip arthroplasty and long bone fracture reduction and osteosynthesis are shown.

[Intestinal stomas--indications, stoma types, surgical technique]

The formation of an intestinal stoma is one of the most frequent operations in visceral surgery. Despite new operative techniques and a more restrictive use of the stoma, the stoma formation remains an often necessary surgical procedure, which results to a dramatic change in the patients' life. The stoma formation and its later closure are associated with a high morbidity. Many complications, such as stoma necrosis, stoma retraction or stoma prolapse, are related to surgical mistakes made during stoma formation. These complications are therefore largely avoidable. The stoma formation needs careful planning together with a professional stoma nursing team. Moreover, it is mandatory that the stoma formation is made with great care and that it meticulously follows the well established surgical principles. A perfectly placed, technically correctly fashioned and easy to care for stoma is essential for a good patients'quality of life.

Computed tomography-based surgical navigation for hip arthroplasty

Component malpositioning and postoperative leg length discrepancy are the most common technical problems associated with total hip arthroplasty (THA). Surgical navigation offers the potential to reduce the incidence of these problems. We reviewed 317 patients (344 hips) that underwent THA using computed tomography-based surgical navigation, including 112 THAs using a simplified method of measuring leg length. Guided by the navigation system, cups were placed in 40.8 degrees +/- 2 degrees of operative abduction (range, 35 degrees -50 degrees) and 30.8 degrees +/- 3.2 degrees (range, 19 degrees -43 degrees) of operative anteversion. We subsequently measured radiographic abduction on plain anteroposterior pelvic radiographs and calculated abduction and anteversion. Radiographically, 97.1 % of the cups were in the safe zone for abduction and 92.4% for anteversion. The mean incision length was less than 8 cm for 327 of the 344 hips. Leg length change measured intraoperatively was 6.6 +/- 4.1 mm (range, -2-22), similar to measurements from the pre- and postoperative magnification-corrected radiographs. Computer assistance during THA increased the consistency of component positioning and allowed reliable measurement of leg length change during surgery.

Hip arthroscopy after previous surgical hip dislocation for femoroacetabular impingement

PURPOSE: The purpose of this study was to examine whether arthroscopic adhesiolysis can relieve symptoms of patients with persistent pain after open surgical hip dislocation for femoroacetabular impingement syndrome without osseous or cartilaginous alterations. METHODS: This study comprised 16 consecutive patients (6 men and 10 women; mean age, 33.5 years [range, 19 to 60 years]) with persistent pain without osseous or cartilaginous alterations after surgical hip dislocation for the treatment of femoroacetabular impingement. At index surgery, all patients had osteochondroplasty of the head-neck junction and resection of the acetabular rim with reattachment of the labrum in 9 cases. All patients had preoperative magnetic resonance imaging-arthrogram and were treated with arthroscopy of the hip. RESULTS: At arthroscopy, all reattached labra were stable. In the cases without preservation of the labrum at the index operation, the joint capsule was attached at the level of the acetabular rim and synovitis was noticed. All patients had adhesions between the neck of the femur and joint capsule or between the labrum and capsule. In 3 patients the arthroscopic procedure was technically limited by massive thickening of the capsule. Overall, 81% of patients (13/16) showed less pain or were pain-free. The Merle d'Aubigné score improved from 13 points preoperatively to 16 points at the last follow-up. CONCLUSIONS: Persistent pain after surgical dislocation of the hip without evidence of cartilaginous and osseous alterations could result from intra-articular adhesions. Hip arthroscopy after previous surgery can be demanding because of scarring. If the adhesions can be released, good results can be achieved. LEVEL OF EVIDENCE: Level IV, therapeutic case series.

Treatment of femoro-acetabular impingement: preliminary results of labral refixation. Surgical technique

BACKGROUND: Recent advances in the understanding of the anatomy and function of the acetabular labrum suggest that it is important for normal joint function. We found no available data regarding whether labral refixation after treatment of femoro-acetabular impingement affects the clinical and radiographic results. METHODS: We retrospectively reviewed the clinical and radiographic results of fifty-two patients (sixty hips) with femoro-acetabular impingement who underwent arthrotomy and surgical dislocation of the hip to allow trimming of the acetabular rim and femoral osteochondroplasty. In the first twenty-five hips, the torn labrum was resected (Group 1); in the next thirty-five hips, the intact portion of the labrum was reattached to the acetabular rim (Group 2). At one and two years postoperatively, the Merle d'Aubigné clinical score and the Tönnis arthrosis classification system were used to compare the two groups. RESULTS: At one year postoperatively, both groups showed a significant improvement in their clinical scores (mainly pain reduction) compared with their preoperative values (p = 0.0003 for Group 1 and p < 0.0001 for Group 2). At two years postoperatively, 28% of the hips in Group 1 (labral resection) had an excellent result, 48% had a good result, 20% had a moderate result, and 4% had a poor result. In contrast, in Group 2 (labral reattachment), 80% of the hips had an excellent result, 14% had a good result, and 6% had a moderate result. Comparison of the clinical scores between the two groups revealed significantly better outcomes for Group 2 at one year (p = 0.0001) and at two years (p = 0.01). Radiographic signs of osteoarthritis were significantly more prevalent in Group 1 than in Group 2 at one year (p = 0.02) and at two years (p = 0.009). CONCLUSIONS: Patients treated with labral refixation recovered earlier and had superior clinical and radiographic results when compared with patients who had undergone resection of a torn labrum. Although the results must be considered preliminary, we now recommend refixation of the intact portion of the labrum after trimming of the acetabular rim during surgical treatment of femoro-acetabular impingement.

Heart rate variability does not discriminate between different levels of haemodynamic responsiveness during surgical anaesthesia

BACKGROUND: Hypnotic depth but not haemodynamic responsiveness is measured with EEG-based monitors. In this study we compared heart rate variability (HRV) in unstimulated patients and stimulation-induced HRV at different levels of anaesthesia. METHODS: A total of 95 ASA I or II patients were randomly assigned to five groups (Group 1: BIS 45(5), remifentanil 1 ng ml(-1); Group 2: BIS 45(5), remifentanil 2 ng ml(-1); Group 3: BIS 45(5), remifentanil 4 ng ml(-1); Group 4: BIS 30(5), remifentanil 2 ng ml(-1); Group 5: BIS 60(5), remifentanil 2 ng ml(-1)). A time- and frequency-domain analysis of the RR interval (RRI) from the electrocardiogram was performed. HRV before induction, before and after a 5 s tetanic stimulus of the ulnar nerve, and before and after tracheal intubation was compared between groups, between stimuli, and between responders to intubation [systolic arterial pressure (SAP) increase >20 mm Hg, a maximal heart rate (HR) after intubation >90 min(-1) or both] and non-responders (anova). RESULTS: Induction of anaesthesia significantly lowered HR and HRV. Mean RRI before stimulation was higher in G3 than in G1, G2, and G4 (P < 0.001), whereas the other HRV parameters were similar. Intubation induced a greater HRV response than tetanic stimulation. The mean RRI after intubation was lower in G3 compared with the other groups and the sd of the RRI after tetanic stimulation was lower in G3 compared with G5. Otherwise, unstimulated HRV and stimulation-induced HRV were similar in responders and non-responders. CONCLUSION: HRV parameters discriminate between awake and general anaesthesia, are different after tracheal intubation and a 5 s ulnar nerve stimulation, but do not discriminate between different levels of haemodynamic responsiveness during surgical anaesthesia.

Endovascular and surgical treatment of spinal dural arteriovenous fistulas

INTRODUCTION: The aim of this retrospective study was to evaluate the clinical outcome of patients with spinal dural arteriovenous fistulas (SDAVFs) that were treated with surgery, catheter embolization, or surgery after incomplete embolization. METHODS: The study included 21 consecutive patients with SDAVFs of the thoracic, lumbar, or sacral spine who were treated in our institution from 1994 to 2007. Thirteen patients were treated with catheter embolization alone. Four patients underwent hemilaminectomy and intradural interruption of the fistula. Four patients were treated by endovascular techniques followed by surgery. The clinical outcome was assessed using the modified Aminoff-Logue scale (ALS) for myelopathy and the modified Rankin scale (MRS) for general quality of life. Patient age ranged from 44 to 77 years (mean 64.7 years). RESULTS: Surgical as well as endovascular treatment resulted in a significant improvement in ALS (-62.5% and -31.4%, respectively, p < 0.05) and a tendency toward improved MRS (-50% and -32%, respectively) scores. Patients that underwent surgery after endovascular treatment due to incomplete occlusion of the fistula showed only a tendency for improvement in the ALS score (-16.7%), whereas the MRS score was not affected. CONCLUSION: We conclude that both endovascular and surgical treatment of SDAVFs resulted in a good and lasting clinical outcome in the majority of cases. In specific situations, when a secondary neurosurgical approach was required after endovascular treatment to achieve complete occlusion of the SDAVF, the clinical outcome was rather poor. The best first line treatment modality for each individual patient should be determined by an interdisciplinary team.