Part 1: Outcome of Posterior Pelvic Ring Injuries and Associated Prognostic Factors - A Five-Year Retrospective Study of One Hundred and Sixty Five Operated Cases with Closed Reduction and Percutaneous Fixation.

PURPOSES: The aim of this study was to evaluate: 1. the outcome of pelvic ring fractures treated by closed reduction and percutaneous fixation, 2. the prognostic factors associated with a poor quality reduction, 3. the prognostic factors associated with ilio-sacral screws misplacement and 4. the prognostic factors associated with nonunion. METHODS: Data from medical charts for all patients admitted with unstable posterior pelvic ring injuries from 2009 to 2013 were extracted. A total of 165 patients with a mean age of 40 years were included. One hundred and five patients were reviewed at a mean of 32 months of follow-up. The prognostic factors analyzed were clinical and radiological factors. Tile B and Tile C pelvic ring fractures were compared and analyzed separately. Then specific statistical analysis was performed using a logistic regression model to eliminate confusion factors. RESULTS: An excellent or good clinical result was achieved for 94 patients (90%). An excellent or good reduction was achieved for 141 patients (85%). Nonunion rate, smoking patients, bad reductions, age of patients and ISS score were significantly higher in Tile C group. To eliminate confusion factors we used a multivariate analysis logistic regression model. Only unstable vertical bilateral posterior injuries (Tile C2 and C3) were independent prognostic factors for unsatisfactory reduction (p = 0.001; OR = 4.72; CI 95% [2.08-16.72]). Screw misplacement was recorded for 30 patients (16%) and sacral dysmorphia was an associated prognostic factor (p = 0.0001; OR = 15.6; CI95% [3.41-98.11]). Nonunion was recorded for ten patients (6%) and smoking was an associated prognostic factor (p = 0.01, OR = 5.12; CI95% [1.1-24.1]). CONCLUSIONS: Posterior pelvic ring fractures treated by closed reduction and percutaneous fixation are associated with excellent/good clinical results if excellent/good reduction and bone healing are achieved without screw misplacement. Bilateral unstable vertical posterior pelvic ring injuries, and sacral dysmorphia are risk factors for bad quality reduction and screw misplacement respectively.

Optimization of perioperative management of proximal femoral fracture in the elderly.

Proximal femoral fracture in elderly subjects is a major event that is life-threatening in the medium-to-long term. Advanced age, male gender and number of comorbidities largely account for high mortality and require geriatric expertise. Protein-energy malnutrition and bone demineralization increase mortality. Mortality can, on the other hand, be reduced by acting on two variables accessible to medical intervention: daily activities and nutritional status. Functional and neurocognitive assessment allow the risk of dependency to be evaluated, and global geriatric work-up can prevent sudden breakdown of homeostasis. In the emergency setting, pain is to be alleviated, polymedication and anticoagulation therapy checked, and instability (notably cardiac and pulmonary) and confusion syndrome screened for on geriatric and anesthesiologic opinions. Surgery should be implemented without delay, within 48hours of admission, preferably using multimodal anesthesia. The technique should be geared to allow early weight-bearing and mobilization. The most comprehensive care plan involves team-work between emergency physicians, surgeons, orthopedic specialists, anesthesiologists, geriatricians, pharmacists, rehabilitation specialists and nursing staff, to reduce mortality and readmission and improve functional results. Post-fracture coordination seeks to prevent falls and further fractures and to treat bone demineralization.

Epidemiology and treatment of acetabular fractures in a level-1 trauma centre: Retrospective study of 414 patients over 10 years.

BACKGROUND: Epidemiological studies of acetabular fractures (AFs) are scarce and, to our knowledge, the most recent one from France, by Letournel and Judet, dates back to 1993. Studies have suggested a decrease in high-energy AFs contrasting with an increase in low-energy AFs due to the longer life expectancy. However, a French case-series study failed to confirm these data. We therefore conducted a 10-year retrospective study in a level-1 trauma centre to: (1) characterise the epidemiological profile of AF; (2) and to describe the treatment strategy. HYPOTHESIS: The epidemiological profile of AF in France is consonant with data from European case-series studies. METHOD: All patients managed for AF between 2005 and 2014 were included in this single-centre retrospective study. All patients were re-evaluated at our centre or another facility 6 months after the fracture. The epidemiological data were compared in the three treatment groups: non-operative, open reduction and internal fixation (ORIF), and total hip arthroplasty (THA). RESULTS: Between 2005 and 2014, 414 patients were admitted for AF. Mean age was 49.4 years (range: 15-101 years). Treatment was non-operative in 231 (56%) older patients, most of whom had low-energy fractures involving the anterior wall. THA with or without acetabular reinforcement and screw-plate fixation was performed in 27 (7%) older patients, most of whom had posterior-wall fractures and experienced postoperative complications (26/27 patients, 96%). ORIF was used in 156 (38%) younger patients, most of whom had high-energy fractures of greater complexity. CONCLUSION: Our results reflect the current indications in AF management. The epidemiological characteristics in our population are comparable to those reported in the few recent European epidemiological studies. To our knowledge, this is the largest French epidemiological study since the landmark work by Letournel and Judet. LEVEL OF EVIDENCE: Level IV, retrospective study.

Posterior tibial slope accuracy with patient-specific cutting guides during total knee arthroplasty: A preliminary study of 50 cases.

BACKGROUND: Patient-specific cutting guides were recently introduced to facilitate total knee arthroplasty (TKA). Their accuracy in achieving optimal implant alignment remains controversial. The objective of this study was to evaluate postoperative radiographic outcomes of 50 TKA procedures with special attention to posterior tibial slope (PTS), which is difficult to control intraoperatively. We hypothesized that patient-specific cutting guides failed to consistently produce the planned PTS. MATERIAL AND METHODS: The Signature™ patient-specific cutting guides (Biomet) developed from magnetic resonance imaging data were used in a prospective case-series of 50 TKAs. The target PTS was 2°. Standardised digitised radiographs were obtained postoperatively and evaluated by an independent reader. Reproducibility of the radiographic measurements was assessed on 20 cases. The posterior cortical line of the proximal tibia was chosen as the reference for PTS measurement. Inaccuracy was defined as an at least 2° difference in either direction compared to the target. RESULTS: The implant PTS was within 2° of the target in 72% of knees. In the remaining 28%, PTS was either excessive (n=10; maximum, 9°) or reversed (n=4; maximum, -6°). The postoperative hip-knee-ankle angle was 0° ± 3° in 88% of knees, and the greatest deviation was 9° of varus. CONCLUSION: These findings support our hypothesis that patient-specific instrumentation decreases PTS accuracy. They are consistent with recently published data. In contrast, patient-specific instrumentation provided accurate alignment in the coronal plane.

Prevalence of protein-energy malnutrition in hospital patients over 75 years of age admitted for hip fracture.

INTRODUCTION: One percent of falls in over-75 years old cause hip fracture (HF). Protein-energy malnutrition (PEM) is associated with falls and fracture. PEM screening and perioperative nutritional management are recommended by the European Society of Parenteral and Enteral Nutrition, yet data on nutritional status in elderly HF patients are sparse. The Mini Nutritional Assessment (MNA) score is presently the most effective screening tool for PEM in over-75 years old. OBJECTIVE: The principal objective of the present study was to determine the prevalence on MNA of PEM in patients aged over 75 years admitted for HF. Secondary objectives were to identify factors associated with PEM and its role as a factor of evolution. MATERIALS AND METHODS: A prospective observational epidemiological study included 50 patients aged over 75 years admitted for HF in an 8-bed orthopedic surgery department with a geriatric follow-up unit. PEM was defined by MNA<17/30. Assessment systematically comprised associated comorbidity (Cumulative Illness Rating Scale-Geriatric [CIRS-G]), cognitive status on the Mini Mental State Examination (MMSE), functional status on activities of daily life (ADL), and mean hospital stay (MHS). Scores were compared on quantitative tests (Student t) with the significance threshold set at P<0.05. RESULTS: Mean age for the 50 patients was 86.1 years (range, 77-94 years). Prevalence of PEM was 28%; a further 58% of patients were at risk for PEM. PEM was associated with elevated CIRS-G (P<0.006), greater numbers of severe comorbidities (P=0.006), more severe cognitive disorder (P=0.005) and functional dependence (P=0.002), and 8 days' longer MHS (P=0.012). DISCUSSION: The present study confirmed the high prevalence of PEM in HF patients aged over 75 years, supporting longer hospital stay. MNA is a diagnostic gold standard, not to be replaced by albuminemia or body-mass index in this perioperative clinical situation. Given the present economic stakes relating to geriatric trauma patients' hospital stay, it is essential to prevent, diagnose and treat PEM in elderly subjects. LEVEL OF EVIDENCE: Level IV; prospective cohort study.

Technique for reduction and percutaneous fixation of U- and H-shaped sacral fractures.

We describe an early reduction and percutaneous fixation technique for isolated sacral fractures. Strong manual traction combined with manual counter-traction on the torso is used to disimpact the fracture. Transcondylar traction is then applied bilaterally and two ilio-sacral screws are inserted percutaneously on each side. Open reduction and fixation, with sacral laminectomy in patients with neurological abnormalities, remains the reference standard. Early reduction and percutaneous fixation ensures restoration of the pelvic parameters while minimising soft-tissue damage and the risk of infection. Decompression procedures can be performed either during the same surgical procedure after changing the installation or after a few days. These complex fractures warrant patient referral to specialised reference centres.

Kyphoplasty versus vertebroplasty in osteoporotic thoracolumbar spine fractures. Short-term retrospective review of a multicentre cohort of 127 consecutive patients.

BACKGROUND: Osteoporotic spine fractures induce a heavy burden in terms of both general health and healthcare costs. The objective of this multicentre study by the French Society for Spine Surgery (SFCR) was to compare outcomes after vertebroplasty and kyphoplasty in the treatment of osteoporotic thoracolumbar vertebral fractures. HYPOTHESIS: We hypothesised that differences existed between vertebroplasty and kyphoplasty, notably regarding operative time and reduction efficacy, from which criteria for patient selection might be inferred. MATERIAL AND METHODS: We conducted a retrospective multicentre review of 127 patients with Magerl Type A low-energy fractures after a fall from standing height between 2007 and 2010; 85 were managed with vertebroplasty and 42 with kyphoplasty. Age was not a selection criterion. We recorded pain intensity, time to management, operative time, kyphosis angle, wedge angle, cement leakage rate, and degree of cement filling. RESULTS: Operative time was 43 minutes with kyphoplasty and 24 minutes with vertebroplasty (P=0.0002). Both techniques relieved pain, with no significant difference. Kyphoplasty significantly improved the wedge angle, by +6°, versus +2° with vertebroplasty (P=0.002). With kyphoplasty, the volume injected was larger and cement distribution was less favourable. Leakage rates were similar. DISCUSSION: Despite the heterogeneity of our study, our data confirm the effectiveness of kyphoplasty in alleviating pain and decreasing deformities due to osteoporotic vertebral fractures. Vertebroplasty is a faster and less costly procedure that remains useful; no detectable clinical complications occur with vertebroplasty, which ensures better anchoring of the cement in the cancellous bone.

Evaluation of a computer-assisted navigation system for anterior cruciate ligament reconstruction: prospective non-randomized cohort study versus conventional surgery.

BACKGROUND: Conventional reconstruction of the anterior cruciate ligament (ACL) is associated with a 15% failure rate. Computer-assisted navigation systems (CANS) have been developed to improve the accuracy of tunnel positioning. HYPOTHESIS: The use of a CANS for ACL reconstruction decreases the rate of failure, defined as IKDC grade C or D, compared to conventional ACL reconstruction. MATERIALS AND METHODS: This prospective multicentre observational non-randomised open study compared two groups of patients requiring arthroscopic ACL reconstruction: one group was managed with a CANS and the other (control group) without a CANS. The primary evaluation criterion was based on the subjective and objective IKDC scores. Inclusion criteria were age older than 18 years and first ACL reconstruction procedure using autologous semitendinosus and gracilis tendons or an autologous bone-patellar tendon-bone graft. Of the 272 included patients, 214 were analysed; 100 were in the control group and 114 in the CANS group. RESULTS: No significant between-group differences were found for the fraction of patients having an IKDC grade A or B (P=0.953), the subjective IKDC score (P=0.77), differential knee laxity at 150 N (1.38 ± 1.79 mm in the control group and 1.77 ± 2.06 mmin the CANS group, P=0.384), graft-type, or graft positioning. DISCUSSION: Our results establish the large-scale feasibility of computer-assisted navigation for ACL reconstruction. However, the main outcomes at 1 year showed no significant differences between patients managed with and without computer-assisted navigation.

Bone transport techniques in posttraumatic bone defects.

INTRODUCTION: The treatment of posttraumatic diaphyseal bone defects (BD) calls on a number of techniques including bone transport techniques: isolated shortening, compression-distraction at the fracture site, shortening followed by lengthening in a corticotomy distant from the site and segmental bone transport. PATIENTS AND METHODS: The multicenter retrospective study combined 38 cases: 22 cases of initial diaphyseal bone defect and 16 cases of secondary diaphyseal BD, sometimes associated with metaphyseal or metaphyseal-epiphyseal BD, involving the humerus, the forearm, the femur and the tibia. These techniques were mainly used on the lower extremity (33 cases), for the most part on the tibia (22 cases) in young men. RESULTS: Bone healing was acquired in 37 cases out of 38 after a mean 14.9 months (range, 6-62 months). A mean 4.3 secondary interventions were required to obtain final union; most notably, a bone graft was necessary at the docking site for the segmental bone transport procedures. DISCUSSION: Many reconstruction techniques can be proposed to treat posttraumatic BD. None responds to all situations. Bone transport techniques have their place and their indications. Isolated shortening is intended for bone loss not exceeding 3cm, notably in the humerus and to a lesser degree in the lower extremity. Shortening associated with lengthening is valuable in the femur and the tibia for bone loss up to 6cm. Segmental bone transport is the only technique that can treat bone defects associated with shortening in the lower limb. For substantial bone loss beyond 10cm, segmental bone transport is particularly indicated. However, these cases of substantial bone loss tend to be resolved by a hybridization of the procedures. The distraction gap of a bone segment can, for example, be prepared using an induced-membrane technique. LEVEL OF EVIDENCE: Level IV. Retrospective study.

Analysis of anatomic positioning in computer-assisted and conventional anterior cruciate ligament reconstruction.

INTRODUCTION: Anterior cruciate ligament (ACL) reconstruction should be anatomic while achieving favorable anisometric behavior to avoid impingement with the femoral notch. Computerization enables these biomechanical conditions to be optimally fulfilled; but what of anatomic positioning? The present study compared the positioning of tibial and femoral tunnels, drilled using either a conventional ACL guide or a navigation system, using the anatomic foot-print areas of the native ACL. MATERIAL AND METHODS: This cadaver study used computerized recording to compare tibial and femoral ACL attachment areas to the positioning of tunnels created either conventionally or under computer-guided navigation. RESULTS: Computer guidance enabled the tibial and femoral tunnels to be systematically positioned within the anatomic area and, as regards the tibial area, within the anterior third near to the medial tibial spine, without femoral notch impingement. Anisometry was in all cases favorable, at a mean 3.3 ± 0.7 mm; using a conventional guide, anisometry was favorable in only 50% of cases, at a mean 5.4 ± 1.2 mm. CONCLUSION: Computer-guided navigation ensured implant positioning within the so-called anatomometric area of the native ACL attachment, avoiding impingement with the femoral notch. LEVEL OF EVIDENCE: Level 2.

Bone regeneration and limb lengthening.

Regeneration of bone in the presence of stable fixation and the maintenance of the osteogenic tissue (marrow, endosteum, nutrient artery, and periosteum) required another factor to stimulation of bone regeneration: incremental distraction produces bone of both endosteal and periosteal origin. The soft tissues undergo to same growth phenomenon. The mechanism of ossification occurs without intermediate fibrocartilage.

Macroscopic and microscopic process of long bone fracture healing.

The growth of each type of callus (cortical, medullary and periosteal) depends on the mechanical condition of fracture fixation (elastic fixation and instability or rigid immobilization), the type of treatment (non-operative, close or open surgical procedure, intra-medullary nailing, external fixation, plate...) and the high or poor quality of soft tissue and the specific characteristics of the local vascularisation.

Anterior cruciate ligament reconstruction: assessment of the hamstring autograft femoral fixation using the EndoButton CL.

UNLABELLED: The objective of this study was to evaluate the clinical and radiological results of a prospective, continuous series of 105 ACL reconstructions using the STG tendons fixed to the femur by an EndoButton CL, with more than 4 years of follow-up. HYPOTHESIS: The subjective and objective clinical results as well as the radiological results (tunnel enlargement) obtained by a cortical, extra-anatomic femoral fixation are at least equivalent to the results obtained with other types of femoral fixation systems. MATERIAL AND METHODS: One hundred and five patients aged with a mean 26 years (range, 12-56 years) were operated on for an anterior cruciate ligament rupture using the same technique and by the same operator: four-strand STG fixed to the tibia by a double fixation--BioRCI-HA screw and staple--and on the femur by an EndoButton CL (Smith and Nephew). The results were assessed at 6 months, 1 and 2 years and then at a mean follow-up of 51 months, both clinically (IKDC, Lysholm, KT-1000) and radiologically (Telos laximetry, tunnel position, and morphological analysis). RESULTS: No complications related to the use of the EndoButton were observed. No additional interference screw was necessary. According to the IKDC laxity classification, 91.4% of the patients were classified in category A or B, nine knees (8.6%) were classified C or D. Four failures required revision with a patellar tendon graft. On the final IKDC score, 63 patients (60%) were classified grade A, 37 grade B (35.3%), four grade C (3.8%), and one grade D (0.9%). On the Telos laximetry, 62 patients (59%) had a differential laxity less than or equal to 2 mm. The mean value was 1.8 mm (range, 0-11). Tibial tunnel enlargement was constant; femoral tunnel enlargement was significant (>2 mm) in 27.6% of the knees. No femoral tunnel diameter modification corresponding to the EndoButton passage was observed. DISCUSSION: The results of this series are comparable to the results of other series. Its reproducibility and the absence of iatrogenic complications for this femoral EndoButton CL fixation make it a top-choice technique, like the corticocancellous graft procedures, but without their disadvantages. No secondary elongation attributable to the EndoButton CL was observed. This femoral fixation procedure appeared necessary and sufficient to providing good mechanical stability for the graft in the femoral tunnel.

Simultaneous bilateral femoral neck fractures secondary to epileptic seizures: treatment by bilateral total hip arthroplasty.

Simultaneous bilateral femoral neck fracture following an epileptic seizure attack are rare. Open reduction and internal fixation remains the most used therapeutic option. Arthroplasty, carrying a high risk of dislocation is less often recommended. We report the favourable evolution of a 49-year-old man who benefited from a single stage bilateral total hip arthroplasty operation for his simultaneous bilateral, femoral neck fractures secondary to a generalized seizure. This nonconsensual choice, in this case, was justified on multiple grounds: surgical care delay longer than 48 hours, substantial bone displacement, borderline bone quality, adequate antiepileptic treatment efficacy and tolerance. A ceramic-on-ceramic bearing surfaces couple, a large-diameter head and a cementless implantation design together should be able to provide an acceptable longevity in a young and active patient.

Assessment of a percutaneous iliosacral screw insertion simulator.

BACKGROUND: Navigational simulator use for specialized training purposes is rather uncommon in orthopaedic and trauma surgery. However, it reveals providing a valuable tool to train orthopaedic surgeons and help them to plan complex surgical procedures. PURPOSE: This work's objective was to assess educational efficiency of a path simulator under fluoroscopic guidance applied to sacroiliac joint percutaneous screw fixation. MATERIALS AND METHODS: We evaluated 23 surgeons' accuracy inserting a guide-wire in a human cadaver experiment, following a pre-established procedure. These medical trainees were defined in three prospective respects: novice or skilled; with or without theoretical knowledge; with or without surgical procedure familiarity. The screw insertion in the human cadaver was performed in two different settings: either without prior training for a first group (G1) or after simulator guidance in the second group (G2). Analysed criteria for each tested surgeon included the number of intraoperative X-rays taken in order to achieve the surgical procedure as well as an iatrogenic index reflecting the surgeon's ability to detect any hazardous trajectory at the time of performing said procedure. RESULTS: An average number of 13 X-rays was required for wire implantation by the G1 group. G2 group, assisted by the simulator use, required an average of 10 X-rays. A substantial difference was especially observed within the novice sub-group (N), with an average of 12.75 X-rays for the G1 category and an average of 8.5 X-rays for the G2 category. In the second sub-group of operators devoid of procedural knowledge (P-), a significant difference was found, since 12 X-rays appeared on average required in the G1 group versus six in the G2 group. Finally, within the sub-group of operators with technical knowledge (T+), a significant difference also was found since an average of 16 X-rays was required in the G1 versus an average 10.8 X-rays in the G2 group. As far as the iatrogenic index is concerned, we were unable to observe any significant difference between the groups. DISCUSSION: Despite some methodological variations, we were able to demonstrate the simulator's efficiency in familiarizing the operator with the use of a 2D imaging system as a first step facilitating the procedure conduct in the real 3D patient environment. Novice surgeons (N) having a good lumbosacral joint anatomy knowledge although devoid of specific surgical technique knowledge were the ones who most benefited from this guiding tool. Analysis of the training data collected during simulator's use helps orientating the prospective surgeon toward possession of not yet acquired learning points. This educational program can easily be extended to any other percutaneous technique requiring fluoroscopic control guidance. LEVEL OF EVIDENCE: Level III prospective diagnostic study.

Superficial femoral artery injury resulting from intertrochanteric hip fracture fixation by a locked intramedullary nail.

UNLABELLED: Iatrogenic vascular injuries are uncommon during the course of proximal femur surgical procedures. We report the case of an 85-year-old female presenting with an intertrochanteric fracture, treated by anterograde (cephalocondylic) intramedullary nailing (Stryker gamma 3 nail) and complicated by a superficial femoral artery laceration at the level of the distal locking screw. Lower limb traction in adduction and internal rotation on the operating table might put at risk the superficial femoral artery during distal screw drilling and insertion. We therefore recommend returning to the neutral position and reducing lower extremity traction after femoral head screw placing and before final distal screw insertion. This technical precaution should limit the risk of superficial femoral artery injury associated with short-nail anterograde intramedullary nailing. TYPE OF STUDY: Level IV retrospective.

Fluoroscopy-based navigation system in spine surgery.

The variability in width, height, and spatial orientation of a spinal pedicle makes pedicle screw insertion a delicate operation. The aim of the current paper is to describe a computer-assisted surgical navigation system based on fluoroscopic X-ray image calibration and three-dimensional optical localizers in order to reduce radiation exposure while increasing accuracy and reliability of the surgical procedure for pedicle screw insertion. Instrumentation using transpedicular screw fixation was performed: in a first group, a conventional surgical procedure was carried out with 26 patients (138 screws); in a second group, a navigated surgical procedure (virtual fluoroscopy) was performed with 26 patients (140 screws). Evaluation of screw placement in every case was done by using plain X-rays and post-operative computer tomography scan. A 5 per cent cortex penetration (7 of 140 pedicle screws) occurred for the computer-assisted group. A 13 per cent penetration (18 of 138 pedicle screws) occurred for the non computer-assisted group. The radiation running time for each vertebra level (two screws) reached 3.5 s on average in the computer-assisted group and 11.5 s on average in the non computer-assisted group. The operative time for two screws on the same vertebra level reaches 10 min on average in the non computer-assisted group and 11.9 min on average in the computer-assisted group. The fluoroscopy-based (two-dimensional) navigation system for pedicle screw insertion is a safe and reliable procedure for surgery in the lower thoracic and lumbar spine.

[Computer assisted orthopedics surgery]. / L'expérience de la navigation chirurgicale dans l'ouest.

Computer-assisted surgery has become commonplace in orthopedic surgery. The number of applications grows steadily as does the number of patients benefiting from these new techniques. The hearty debates heard when these techniques were first introduced have now given way to more evidence-based evaluation. Our objective here is to continue this approach by presenting our six-year experience with navigation. We will not discuss the theoretical background of these technologies nor attempt to present an exhaustive review of the literature but rather focus attention on surgical skills acquired by a group of surgeons working in a wide range of areas. The common point is that all have now integrated computer-assisted navigation into their routine surgical practices including: a) first-intention and revision knee arthroplasty; b) hip arthroplasty; c) anterior cruciate ligament surgery; d) proximal tibial osteotomy; e) shoulder arthroplasty. We will terminate this round table with a presentation of future technological advances and propose our advice for an increasingly widespread use of these new techniques.

[Accuracy measurements of acetabular cup positioning using CT less navigation]. / Protocole d'évaluation du risque d'erreur dans le positionnement cotyloïdien par navigation sans imagerie tomodensitométrique préopératoire.

PURPOSE OF THE STUDY: Standard methodology is lacking for evaluating the accuracy of surgical navigation systems. The purpose of the present study was to propose a new approach to error measurements of an image-free navigation system used for total hip arthroplasty. MATERIAL AND METHODS: This new approach evaluates the overall accuracy of the system and quantifies the influence of clinical application on this global error. The majority of hip navigation systems use the anterior pelvic plane as part of the reference system. With image-free systems, anatomic pelvic landmarks must be acquired intraoperatively in order to define the anterior pelvic plane. This step could potentially introduce a significant error for navigation. Two studies were performed to measure this error, one on patients and the other on pelvic phantoms. Both used the difference between the intraoperative cup orientation, as displayed by the navigation system and the postoperative cup position, measured on computer tomography (CT) data. The CT measurements used the same reference system as the navigation system. RESULTS: The intraobserver measurement variability ranged from 48.4 degrees to 49.5 degrees for cup abduction and from 12 degrees to 13.5 degrees for anteversion. The interobserver variability ranged from 47.5 degrees to 19 degrees for cup abduction and from 11.8 degrees to 13.8 degrees for anteversion. Overall errors were calculated for cup abduction and anteversion. Cup navigation was accurate on pelvic bone phantoms. The anteversion error ranged from 0 degrees to 2.5 degrees (mean 0.9 degrees, standard deviation 0.7 degrees). For the clinical study, abduction errors ranged from 2.1 degrees to 16.7 degrees. The mean abduction error introduced by the acquisition of anatomic landmarks was 7.2 degrees. DISCUSSION: The proposed simple clinical end-to-end accuracy evaluation model provides the surgeon with sufficiently accurate information. The evaluation model was able to identify and more importantly to quantify the clinically induced error. This study proves that ameliorating the reference system acquisition would improve the system's overall accuracy.