Introduction: The common belief is that navigation-assisted TKR improves the surgical accuracy and reduces outliers, albeit increasing the operating time. We conducted a detailed study of the published studies with four main criteria:

Reduction of outliers in the placement of implants.

Methods: We performed a computerized search of the PubMed repository and a manual search of the proceedings of the International Society for Computer Assisted Orthopaedic Surgery (CAOS, 2001–05) to include all studies that presented clinical data of the results of this procedure. A total of 139 clinical studies were found, a total of 7,158 patients who underwent navigation-assisted TKR.

Results: Of the 139 studies, 39 studies presented data showing a reduction of outliers of the post-operative mechanical axis in the 180±3° range. 2,130 out of 2,401 (89%) patients operated with navigation were within this range. 27 out of the 39 studies compared the postoperative alignment of the navigated technique to that of the non-navigated technique. In the non-navigated technique, only 1,325 out of 1,880 (71%) patients were in that range, close to the published 74–75% for conventional TKR studies.

Regarding the operating time with navigation, 32 studies report an average increase of 21 min. (range 6– 48 min.), or about 20% than conventional TKR.

One of the perceived benefits of using extramedullary jigs in navigation-assisted TKR is thought to be reduction of blood loss. However, of the 15 studies that address this issue, 10 (67%) found no significant difference compared to the conventional technique. Regarding post-operative functional and/or pain scoring, 12 (80%) out of 15 studies found no statistically significant differences between navigated and non-navigated techniques.

Conclusions: The published clinical data so far shows that navigated-assisted TKR provides good alignment of the implants and a reduction of outliers from one in four to at most one in ten at the expense of 15–20 min. (about 20%) increase in operating time. No significant advantage was found for blood loss or functional/pain scoring. From a public health viewpoint, the increased cost of the navigated procedure may very well be compensated by the reduction of future revisions.

Introduction: Fluoroscopy-based navigation systems enables surgeons to place implants with a simultaneous multi-planar monitoring. Percutaneous fixation of femoral neck fractures is an example of the growing usage of these systems in orthopedic trauma surgery. Growing evidence suggests that the accuracy of screw placement might affect the fracture outcome.

Methods: Between 2/2001 and 8/2005, 80 patients underwent internal fixation of femoral neck fractures using computerized navigation system. Three cannulated screws were implanted in an inverted triangle formation. The average patient’s age was 62±20 years (range 11–88), and 12 patients were under the age of 40 years. 53 patients were female, 27 male. 68 patients sustained the fracture due to a simple fall, 4 fell from high ground, 3-bicycle injuries, 2 due to motor vehicle accidents, and 3 patients suffered from insufficiency fractures with no trauma. The data includes results for both undisplaced fractures and fully displaced fractures which underwent closed reduction.

Results: The average length of hospital stay was 6.3±4 days (range 1–19). The average operating room time was 82±22 minutes (range 30–135), this including the preparation of the patient and instrumentation. Complications included one case of infection which necessitated long term antibiotic treatment, four patients requiring hip arthroplasty due to avascular necrosis of the femoral head, and one patient who underwent hip arthroplasty due to osteoarthritis. The total failure rate is 6%.

Conclusions: Computerized navigation for the internal fixation of subcapital femoral neck fractures allows improved screw positioning, which may reduce fracture complications, and provides reduced radiation to both the surgeon and the patient.

Introduction: To enable navigated-assisted orthopedic surgery, a reference frame must be rigidly fixed to a stable bony structure. This may create technical obstacles and wound complications. Instead, we propose to attach the reference frame to the fracture table.

Methods: The study population consisted of 10 patients who underwent fixation of subcapital femoral neck fracture with three cannulated screws, using fluoroscopy-based navigation. Step 1 – the patient was positioned on a fracture table and the reference frame was attached to the iliac crest. Three guide wires were inserted under fluoroscopy-based navigation. 2 – New fluoroscopic images were acquired. 3 – Navigated drill guide placed over each guide wire to record final navigated drill guide position – these images include actual guide wire positions and the trajectories of the navigated drill guide. Navigation accuracy was validated, measuring translational and angular deviations of the virtual trajectory from the implant on the same fluoroscopic image in anteroposterior and lateral views. 4 – The reference frame was removed from the iliac crest and attached to the fracture table. Step 3 was then repeated.

Results: The translational deviation of the virtual trajectory from the inserted guide wire when the reference frame was attached to the iliac crest was not statistically significant from the deviation when it was attached to the fracture table. Angular differences were also not statistically significant.

Conclusions: In our experience, attaching the reference frame to the fracture table instead of to the iliac crest allows for similar accuracy of the navigation process with the possible benefit of reducing patient morbidity.

Introduction: Several factors render plain X-ray radiographs of the hip unsuitable for bone mineral density measurements, mainly variability in X-ray exposure levels and soft tissue surrounding the bone. We present modification of proximal femur digital radiographs to compensate for these interfering factors.

Methods: The study population consisted of 99 women, in three groups: 1 – elderly, sustaining a fracture of the neck of the femur. 2 – elderly, without a fracture. 3 – young. Each patient’s hip was radiographed with a brass step-wedge for standard reference. Dual-Energy X-ray Absorptiometry (DEXA) of the same hip was performed. On each radiograph, Regions Of Interest (ROIs) of the proximal femur were determined in concordance with ROI of the DEXA, together with three soft tissue regions surrounding the bone. Mean gray level was measured for each ROI.

Results: The difference in gray level of the ROI within the proximal femur was not statistically significant between the groups. Correction of bone gray level to exposure level by dividing the gray level of the ROI to that of the step wedge, resulted in statistically significant difference between group 1 and either group 2 or group 3. Similar results were obtained by correction of bone gray level to soft tissue gray level. Using this method, multiple R² of 0.62 was found predicting the DEXA value from the gray level of each ROI.

Conclusions: After correction to the exposure level and to the soft tissue surrounding the bone, a plain digital radiograph of the pelvis can provide valuable information concerning the bone mineral content of the proximal femur. These preliminary results warrant further research aimed at exploring the potential value of this fast, accessible and relatively inexpensive technique to diagnose osteoporosis and the prediction of future fractures.

Introduction: The most widely accepted method for measuring bone mineral density (BMD) is Dual-energy X-ray Absorptionmetry (DXA). However, the need for relatively expensive equipment and trained personnel lower the accessibility of DXA as a routine screening tool. Plain pelvic X-ray radiography is a simple and inexpensive examination. In principal, the gray level of the bone in the X-ray radiograph is related to BMD. However, several factors render plain X-ray radiographs of the hip unsuitable for BMD measurements, mainly the variability in X-ray exposure levels and the soft tissue surrounding the bone. In this study, we aimed to develop new modifications of plain X-ray radiography of the proximal femur.

Patients and methods: The study population consisted of 18 women with an average age of 77 years (range 57–96 years) who were hospitalized due to a low-energy fracture of the neck of the femur. Each patient’s contralateral hip was radiographed with an aluminium step-wedge positioned near the hip as a standard reference, using a computerized radiography system. A DXA examination of the same hip followed the plain radiograph. On each radiograph, regions of interest (ROI) were determined in concordance with the ROI of the DXA examination. The mean gray level was measured for each ROI. The neck-shaft angle and the femoral head diameter were also measured.

Results: Comparing the gray levels of the plain radiograph with the BMD levels obtained by the DXA revealed a coefficient ratio of R=0.499. Correction of the gray levels using the step wedge as a standard reference revealed a ratio of R=0.576. If further correction was made with measurement of the soft tissue gray levels, a ratio of R=0.708 was obtained. Using the anatomical measurements (neck-shaft angle and femoral head diameter), a ratio of R=0.948 was obtained.

Conclusion: This study shows that a plain digital radiograph of the pelvis can provide valuable information concerning the bone mineral content of the proximal femur, which is comparable to the results of the DXA examination. Ultimately, the research can lead to the development of a fast, available and relatively inexpensive technique to diagnose osteoporosis.

Introduction: Bone strength is determined by several factors including bone mineral density and the geometrical structure of bone tissue. Plain X-ray is not used regularly for bone mineral density measurements due to different x-ray exposure used for each patient. The different radiation energies have major effects on the optical density of the obtained films. Therefore dual energy X-ray absorptiometry (DEXA) is the golden standard for bone density estimation. However it is relatively expensive and relatively inaccessible.

Objective: To evaluate a new computerized analysis of digitized plain radiographs of the proximal femur to allow the evaluation of bone mineral density in human subjects.

Material and Methods: 14 people hospitalized for proximal femoral fracture had their uninvolved proximal femur BMD estimated with a DEXA in the 5 typical regions defined by the DEXA test. Plain proximal femur radiographs of these patients were taken with a standard wedge and digitized into the computer to generate a digital image. The gray levels in the digital image were analyzed and normalized to yield the mineral content at the 5 regions defined by DEXA. The data obtained were correlated with the DEXA results.

Results: The correlation between BMD (DEXA) and gray level measurement of the proximal femur (R=0.261) was not significant. This correlation was significantly improved after modification of the gray levels to 0.549 (P< 0.032).

Conclusion: This computerized analysis and modification of gray levels in digitized radiographs improved significantly the possibility to evaluate bone mineral density of the proximal femur from plain X-rays.