Optimal entry point for antegrade femoral intramedullary nailing (IMN) remains controversial in the current medical literature. The definition of an ideal entry point for femoral IMN would implicate a tenseless introduction of the implant into the canal with anatomical alignment of the bone fragments. This study was undertaken in order to investigate possible existing relationships between the true 3D geometric parameters of the femur and the location of the optimum entry point. A sample population of 22 cadaveric femurs was used. Computed-tomography sections every 0.5 mm for the entire length of femurs were produced. These sections were subsequently reconstructed to generate solid computer models of the external anatomy and medullary canal of each femur. Solid models of all femurs were subjected to a series of geometrical manipulations and computations using standard computer-aided-design tools. In the sagittal plane, the optimum entry point always lied a few millimeters behind the femoral neck axis (mean=3.5±1.5 mm). In the coronal plane the optimum entry point lied at a location dependent on the femoral neck-shaft angle. Linear regression on the data showed that the optimal entry point is clearly correlated to the true 3D femoral neck-shaft angle (R2=0.7310) and the projected femoral neck-shaft angle (R2=0.6289). Anatomical parameters of the proximal femur, such as the varus-valgus angulation, are key factors in the determination of optimal entry point for nailing. The clinical relevance of the results is that in varus hips (neck-shaft angle • 120o) the correct entry point should be positioned over the trochanter tip and the use stiff nails is advised. In cases of hips with neck-shaft angle between 120o and 130o, the optimal entry point lies just medially to the trochanter tip (at the piriformis fossa) and the use of stiff implants is safe. In hips with neck-shaft angle over 130o the anatomical axis of the canal is medially to the base of the neck, in a “restricted area”. In these cases the entry point should be located at the insertion of the piriformis muscle and the application of more malleable implants that could easily follow the medullary canal should be considered

Purpose: This cadaveric study examines how changes in femoral entry point for intramedullary instrumentation of total knee replacements affects femoral component positioning. Methods: Twelve cadaveric lower limb specimens with intact hip, knee and ankle joints were obtained. Total knee navigation instrumentation was secured. Anatomical landmarks required for axes generation were obtained. An initial entry point was made at the center of the distal femur. An intramedullary rod was the introduced into the femur. Five and seven degree cutting blocks were placed onto the rod and positioned against the distal femur with the rotation parallel to the epicondylar axis. The navigation system was then used to generate a varus/valgus angle and flexion/extension angle with respect to the previously generated femoral mechanical axes. This allowed determination of an angle at which the distal femoral cutting block would need to be set to make a neutral distal femoral cut. The guide rod was removed and reinserted five times and measurements recalculated. Data was then collected with entry points 5mm medial, 5mm anterior and 5mm medial and anterior to the initial entry point. Results: There was no significant difference in varus/ valgus angle with a central compared with 5mm anterior entry point and no difference with a 5mm medial versus 5 mm medial and anterior entry point. The valgus angle required to give a neutral distal femoral cut with a central entry point was 4.98o (SD 0.91o; range 3.5o–6.0o). The valgus angle for a 5mm medial entry point was 6.92o (SD 0.97o, range 5.5o–8.0o). With regards to the sagittal plane a 5mm anterior translation of the entry point changed the flexion/extension angle by 1.58o (SD 0.52o, range 0.5o–2.5o). Conclusions: Small changes in the entry point can significantly affect component alignment. When moving more medial with the entry point a more valgus angle is required for the cutting block. An entry point at the deepest point of the trochlea may be more reproducible than an anteromedial one but requires a valgus cutting block closer to 5 degrees. Funding: Commerical funding. Funding Parties: Stryker

Introduction: Restoring normal mechanical axis is one of the key goals of the total knee arthroplasty (TKA). The majority of the surgeons resect the tibia perpendicular to its axis in the coronal plane, then use an intra-medullary jig inserted through the centre of the knee or slightly medial to centre of the knee to resect the distal femur at a 6 or 7degree valgus angle. The aim was to establish the safety of using a predetermined valgus angle (VA) and entry point (EP) in the primary TKA. We also studied the relationship between the VA and EP to the height, weight and BMI of the patient. Materials and Methods: We studied 125 long leg radiographs of 125 patients who underwent TKA under the care of senior author. All the radiographs were taken in the preoperative clinic with knee in full extension and patella facing forward. The radiographs were used to measure the valgus angle and entry point of the femur. The patients with VA between 6–7 degrees and EP at the centre were defined as normal group and rest were defined as outliers. Results: The VA ranged from 4 to 9.5 degrees (with a mean of 6.8 and SD 1.11). Only 66 (53%) knees had the VA between 6 and 7 degrees. The EP ranged from 30mm medial to 18mm lateral to the centre of the knee with a mean of 7.7mm medial to the centre of the knee (SD 6.1). The EP was at the centre of the knee in 31 (24.8%) knees and lateral to the centre in 19 (15.2%) knees. Only 14 (11.2%) knees were in the normal group. Overall there was no significant relationship between the EP and VA to the height, weight or BMI of the patient at p-value > 0.001. Conclusions: The resection of distal femur using the predetermined valgus angle, the predetermined entry point is not a safe practice in TKA. The long leg radiographs of the knee should be studied to identify the outliers. In future computer-assisted surgery and digitalisation of the images may obviate the need for this. However, it may be prudent though to use pre-operative templating of long leg radiographs during the learning curve of computer assisted surgery as well

Introduction: Appropriate femoral component alignment is important for long-term survival of total knee arthroplasty (TKA). Valgus angle of femoral component is recommended as the angle between mechanical axis and anatomical axis of the femur. Intramedullary guide system is widely used for determining the valgus positioning of femoral component. Entry point of intramedullary guide is one of the key factors for determining valgus angle of femoral component. Some investigators have shown appropriate entry points of intramedullary guide, however, it is still unclear. In this study, appropriate entry point of intramedullary guide system was calculated using three-dimensional digital templating software “Athena” (Soft Cube, Osaka, Japan). Method: Forty-one knees in 34 osteoarthritis patients except valgus deformity (30 females and 4 males, mean age 75.1 years) received TKA and were simulated using “Athena” from January 2009 to March 2009. All cases were grade III or IV in Kellgren-Lawrence index. Radiograph and CT scan image were used for determination of appropriate entry point of femur using “Athena”. The anatomical axis of femur was defined as a line connecting the midpoints of femoral AP and lateral diameter, at 60 mm and 110 mm proximal to the center of intercondylar notch. Two coordinate systems were configured as representation of entry points. One was at the center of intercondylar notch defined as the point of origin in axial view of CT image and the line parallel to the clinical epicondylar axis (cTEA) defined as X-axis. Another coordinate system was the same point of origin but parallel to the line between trochlear groove and the center of intercondylar notch (AP line) defined as Y-axis. Result: In the coordinate system that defined the cTEA as the X-axis, the average of entry point was 0.3± 0.30 mm medial (range, −4.8~ 4.7mm) and 11.6 ± 0.52mm anterior (range, 3.1~ 16.5mm) to the center of intecondylar notch. In the other coordinate system that defined AP line as the Y-axis, the average of entry point was 2.6± 0.29 mm medial (range, −1.5~ 6.3mm) and 11.2±0.52 mm anterior (range, 2.8~ 16.0mm) to the center of intercondylar notch. Discussion: In this study, the appropriate entry point of intramdullary guide was slightly medial and about 11mm anterior to the center of intercondylar notch on average. However, individual entry point varied considerably in distance. These data indicates that it is important to simulate the appropriate entry point of intramedullary guide in preoperative planning

Aim: To evaluate time of union and functional recovery of the shoulder joint in humeral shaft fractures treated with antegrade intramedullary nailing. Methods: During 1998–2002, 29 patients (16 male and 13 female, mean age 43.7 years) with humeral shaft fractures underwent antegrade, proximal locked, intramedullary nailing. A modified extra-articular entry point, 1 cm below the greater tuberosity, was used to avoid rotator cuff damage. The nail, after accurate measurement of its length and proximal metaphysis enlargement up to 10 mm, was impacted into the narrow, cone-shaped, distal part of the humerus, without the necessity of distal screw interlocking. Passive motion of the shoulder joint was initiated from the 2nd postoperative day and active assisted exercises after the 2nd postoperative week. Results: Mean follow up period was 27 months. Solid callus formation was noted in all fractures, between the 14th and 18th postoperative week. No cases of intra-operative fractures, nerve irritation, rotational instability, nail migration and loss of distal impaction were noted. Mean Constant-Murley score was 93 points at the 16th postoperative week. Conclusion: Antegrade intramedullary nailing is a reliable and beneficial procedure for the treatment of humeral shaft fractures, regarding union and functional recovery of the arm. The extra-articular entry point should be preferred to avoid rotator cuff and articular surfaces damage whereas the accurate measurement of the nail length and the firm impaction of it at the olecranon fossa makes distally interlocking unnecessary, decreasing significantly the overall operative time and the associated complications

Purpose. Femoral shaft fractures are routinely treated using antegrade intramedullary nailing under fluoroscopic guidance. Malreduction is common and can be due to multiple factors. Correct entry point identification can help minimize malreduction and the risk of iatrogenic fracture. This study aims to compare landmark identification used to guide nail entry, the piriformis fossa (PF) and the trochanteric tip (T), via computer navigation and conventional fluoroscopy. Method. The location of the PF and T were digitized under direct visualization with a three-dimensional scribe on ten, fresh-frozen cadaveric right femora (two male, eight female) by three fellowship trained orthopaedic surgeons. To estimate inter- and intraobserver reliability of the direct measurements, an intraclass correlation coefficient was calculated with a minimum of two weeks between measurements. Under navigation, each specimen was draped and antero-posterior (AP) and lateral radiographs of the proximal femur were taken with a c-arm and image intensifier. The c-arm was positioned in a neutral position (0 for AP, 90 for lateral) and rotated in 5 increments, yielding a range of acceptable images. Images, in increments of 5, within the AP range (with a neutral lateral) were loaded into a navigation system (Stryker, MI). A single surgeon digitized the T and PF directly based on conventional fluoroscopy, and again directed by navigation, yielding two measurements per entry point per specimen. This was repeated for the lateral range. Hierarchical linear modelling and a Wilcox rank test were used to determine differences in accuracy and precision, respectively, in the identification of PF and T using computer navigation vs. conventional fluoroscopy. Results. The average range of suitable images for both the AP and lateral images was 29 (range of 25 to 30). The location of the PF and T was found to be reliable for a single observer (0.98 and 0.99) and between observers (0.96 and 0.93). Similar accuracy was found in identifying PF under navigation and fluoroscopy (0.05 to 1.4 cm and 0.1 to 1.5 cm respectively, p = 0.26), whereas improved accuracy was found for T using fluoroscopy (0.07 to 2.5 cm) as compared to navigation (0.2 to 2.2 cm, p < 0.001). For both the PF and T, the navigation-based points had greater precision than those selected by fluoroscopy alone (p = 0.001 and p = 0.024). Conclusion. The ideal entry point, under direct visualization, was highly repeatable, indicating that the surgeons could identify their targeted point of entry for both the PF and T. However, there is an arc of approximately 30, through which acceptable AP and lateral images can be obtained. Throughout this range, the location of the PF and T can vary up to 1.5 and 2 cm, respectively. Navigation was less accurate than fluoroscopy in the T selection, yet had greater precision for both points. Thus, while navigation may decrease accuracy in selection of the T, it is more repeatable overall and equally accurate in selecting the PF

To quantify bone-nail fit in response to varying nail placements by entry point translation in straight antegrade humeral nailing using three-dimensional (3D) computational analysis. CT scans of ten cadaveric humeri were processed in 3D Slicer to obtain 3D models of the cortical and cancellous bone. The bone was divided into individual slices each consisting of 2% humeral length (L) with the centroid of each slice determined. To represent straight antegrade humeral nail, a rod consisting of two cylinders with diameters of 9.5mm and 8.5mm and length of 0.22L mm and 0.44L mm respectively joined at one end was modelled. The humeral head apex (surgical entry point) was translated by 1mm in both anterior-posterior and medio-lateral directions to generate eight entry points. Total nail protrusion surface area, maximum nail protrusion distance into cortical shell and top, middle, bottom deviation between nail and intramedullary cavity centre were investigated. Statistical analysis between the apex and translated entry points was conducted using paired t-test. A posterior-lateral translation was considered as the optimal entry point with minimum protrusion in comparison to the anterior-medial translation experiencing twice the level of protrusion. Statistically significant differences in cortical protrusion were found in anterior-medial and posterior-lateral directions producing increased and decreased level of protrusion respectively compared to the apex. The bottom anterior-posterior deviation distance appeared to be a key predictor of cortical breach with the distal nail being more susceptible. Furthermore, nails with anterior translation generated higher anterior-posterior deviation (>4mm) compared to posterior translation (<3mm). Aside from slight posterolateral translation of the entry point from the apex, inclusion of a distal posterior-lateral bend into current straight nail design could improve nail fitting within the curved humeral bone, potentially improving distal working length within the flat and narrow medullary canal of the distal humeral shaft

The objective of this study was to analyze the biomechanical effect of an implanted ACL graft by determining the tunnel position according to the aspect ratio (ASR) of the distal femur during flexion-extension motion. To analyze biomechanical characteristics according to the ASR of the knee joint, only male samples were selected to exclude the effects of gender and 89 samples were selected for measurement. The mean age was 50.73 years, and the mean height was 165.22 cm. We analyzed tunnel length, graft bending angle, and stress of the graft according to tunnel entry position and aspect ratio (ratio of antero-posterior depth to medio-lateral width) of the articular surface for the distal femur during single-bundle outside-in anterior cruciate ligament reconstruction surgery. We performed multi-flexible-body dynamic analyses with wherein four ASR (98, 105, 111, and 117%) knee models. The various ASRs were associated with approximately 1-mm changes in tunnel length. The graft bending angle increased when the entry point was far from the lateral epicondyle and was larger when the ASR was smaller. The graft was at maximum stress, 117% ASR, when the tunnel entry point was near the lateral epicondyle. The maximum stress value at a 5-mm distance from the lateral epicondyle was 3.5 times higher than the 15-mm entry position and, the cases set to 111% and 105% ASR, showed 1.9 times higher stress values when at a 5-mm distance compared with a 15-mm distance. In the case set at 98% ASR, the low-stress value showed a without-distance difference from the lateral epicondyle. Our results suggest that there is no relationship between the ASR and femoral tunnel length, A smaller ASR causes a higher graft bending angle, and a larger ASR causes greater stress in the graft

Introduction: Correct alignment in both coronal and sagittal planes has been shown to be associated with longevity of total knee arthroplasty. The majority of procedures are performed using an intramedullary rod with a femoral cutting jig, with a 5°–7° offset depending upon the anatomical and mechanical axes. The cutting jig rotates around the rod and therefore the rotational alignment of the jig will also affect the cut and final component position (in addition to the rod entry point). It is interesting that rotational alignment of the femoral component is often assessed after the distal resection has been made. The distal resection plane determines the final position of the femoral component, influences patellar tracking and medial/lateral, flexion/extension balancing. This study measures the resultant effect on the distal femoral resection when entry point and jig rotation are varied. Materials and Methods: The distal femoral resection was carried out in sawbones with three different entry points (central, inferior and superolateral) in neutral alignment and rotations of 10° (internal and external) about the transepicondylar axis. The resulting plane of the cut was assessed by a graphical method measuring the changes in orientation of the alignment rod in space before and after the distal cut. A computer navigation system was used to measure the varus/valgus and flexion/extension angles of the distal cut. This experiment was done thrice, in a total of 27 sawbones and the average values were recorded. Results: The results varied considerably in the sagittal plane with central and inferior entry points. Internal rotation of the jig around a central entry point produced hyperextension (mean 3.3°) and external rotation caused flexion (mean 1.8°). Using an inferior entry point, flexion of the distal plane improved from an average 3° in neutral rotation to 1.6° on internal rotation; external rotation worsened flexion to an average of 4.3°. The angles digressed in both sagittal and coronal planes with a superolateral entry point; rotations of the distal cutting jig caused hyperextension (maximum of 7.5°). Coronal alignment ranged from 4.5° of varus to 5° of valgus in neutral alignment and rotations around a superolateral entry point. Conclusion: The study demonstrates that there is a possibility of a compound error from misplaced entry point and that malrotation prior to distal resection is real. This error would invariably be extrapolated in the subsequent steps of conventional knee arthroplasty. Computer assisted arthroplasty may have a role in avoiding this surgical error

Aim: End result study of closed intramedullary nailing of humerus fractures. Materials & methods: Between 1995–2003, 42 patients with fracture of the humeral shaft, were selected to be treated by I.N. The average age was 48 years old (17years–82years) The Selection criteria were: α) loss of closed reduction (24 patients), b) pathological fractures (5 patients), c) non-union following external fixation (2 patients) and d) delay of union (7 patients). The intramedullary nail was inserted through a proximal entry point via a transdeltoid incision. In 25 cases the entry point was below the greater tuberosity to avoid rotator cuff injury and in 18 cases the entry point was intraarticular. All nails were locked either proximal (41) or distally (1). Open technique was required for 21 cases. Passive full range of motion of elbow and shoulder joint was encouraged after the second postoperative day. Active assisted exercises were initiated the second postoperative week. Bone healing was confirmed by clinical and radiological findings. Shoulder mobility was evaluated by the Constant-Murley scoring system. Results: The average follow-up time was 21 months (9 months–8 years).All fractures were finally healed. The average healing time was 13 weeks (8weeks–13weeks). Patients with extraarticular entry point of the nail had full passive shoulder motion between the 2th and the 4th postoperative week, whereas patients with intraarticular nail application presented delayed passive shoulder motion with final limitation of the normal range of motion. Seven patients had painful shoulder motion 3 months postoperatively. There were 4 patients with neurapraxia of the radial nerve installed posttraumatic, who had full recovery 3 months later. There was one proximal migrated nail, which required revision. None of the patients required nail removal. Conclusions: Intramedullary nailing of humeral shaft fractures seems to be a reliable method of treatment. Shoulder mobilization after anterograde insertion of the nail can be easily restored with proper choice of entry point and proper physiotherapy program. The advantages of this method include: shorter operative time, less blood loss, small incision with minimal soft tissue damage. Extraarticular nail insertion should be the entry point of choice as there is no trauma to the rotator cuff

The aim of this study was to evaluate whether using a predetermined entry point and standard value for valgus cut could restore normal mechanical axis of the TKA. The study included 125 consecutive patients, who underwent TKA under care of the senior author (NJD). Details of height, weight, BMI were noted. All the radiographs were taken with the patient standing, with the knees in maximum extension, with the patella facing forward. The long leg radiographs were evaluated and the mechanical axis and anatomical axis were marked. The entry point (EP) and the angle between the anatomical and the mechanical axis of the femur ware measured, which is valgus angle of distal femoral cut (VA). Statistical analysis was done using SPSS (Table 1). Proportion of the cases with VA less than 6 degrees or more than 7 degrees were identified. Similarly cases with EP distance less than 0 and more than 5mms were also identified. Cases with VA of 6–7 degrees and EP 0–5mms were identified as one group. Correlation was performed using nonparametric tests. The results revealed the angle between the anatomical and the mechanical axis ranges from 4 to 9.5 degrees (mean 6.8 degree and standard deviation 1.11 degree). Only 53% had an angle of between 6 and 7 degrees, with 7% of knees having an angle of less than 5 degree or greater than 8 degrees. The site of entry of the jig showed variation from 30mms medial to the centre to 18mms lateral to the centre with the mean entry point of 5.04mms medial to centre of the notch, with a standard deviation of 8.5mms. Overall only 33% of the knees templated would have an optimal femoral jig placement and distal femoral angle cut with an entry point in the centre of the notch or up to 5mms medial to centre and a distal valgus cut of between 6 and 7 degrees. The author feel this study gives evidence that if the mechanical axis is to be restored then long leg pre-operative radiographs should be performed and used as a key component to the pre-operative plan. Table 1. Spearman’s rho correlations, between the valgus angle and entry point to the height, weight and BMI of the patients

Introduction. Bernese periacetabular osteotomy (PAO) repositions the acetabulum to increase femoral head coverage (FHC) in hip dysplasia. Currently, there is a paucity of objective peri-operative metrics to plan for optimal acetabular fragment repositioning. The MSk Lab Hip 3D Planner (MSkL-HP) measures acetabular morphology and simulates PAO cuts to achieve optimal FHC. We evaluated how adjusting location and orientation of cutting planes can alter FHC. Method. MSkL-HP simulated 274 feasible PAOs on four dysplastic hips. Femoroacetabular anatomy was landmarked to simulate cutting planes. Posterior column and ischial cuts were standardised, whilst iliac and pubic cut combinations varied. The slope of the iliac cut was either neutral (aligned to pelvis), exit point 5mm above the entry point (+5), or 5mm below (-5). The slope of the pubic cut was either 90°, 50°, or 70° (medial-to-lateral). Iliac and pubic cuts were simulated 0, 5 and 15mm - distal and medial – to a classic cut. Outcome measures were achieved LCEA, Tönnis, FHC and % bone overlap at the pubic cut. Targets were LCEA >30°, Tönnis angle <10°, and FHC >70% and minimum bone overlap ≥10%. Results. All feasible PAOs resulted in improvement from pre-operative metrics. Personalised cutting planes provided greater benefit than standard planes. Kruskal Wallis tests showed that the iliac cut at 5mm or 15mm resulted in a greater LCEA and lower Tönnis compared to the classic cut (p<0.05). Changing location of the pubic cut, and slope of the iliac and pubic cuts did not significantly affect LCEA and Tönnis in all hips (p<0.05). Cut combinations optimising metrics were associated with a lower % pubic cut overlap. Conclusion. MSkL-HP feasibly and reliably planned personalised PAO, measuring pre-operative and simulated post-operative objective metrics. Patient-specific pubic and iliac cuts enable greater correction whilst maintaining bone overlap. Further simulations on patients with varying morphology may improve standard techniques

Introduction and Aims: C1 lateral mass screw fixation offers a powerful alternative biomechanical fixaion for upper cervical disorders. The anatomical constraints to this fixation have not been described yet and are essential to ensure avoidance of neurovascular damage. Method: Fifty patients (including five patients with rheumatoid arthritis) underwent upper cervical CT scans. Analysis of these CT scans involved use of calibrated scan measurements to identify the midpoint of the posterior lateral mass, the dimensions of the lateral mass, the direction of optimum screw passage, the position of the vertebral foramen at C1 and the ideal entry point for lateral mass screw fixation. Results: The average length of screw within the lateral mass was 20mm with 13.5mm of screw not in bone, behind the lateral mass, but necessary to allow rod placement posteriorly adjacent to other fixation points. The safest entry point was directly beneath the medial edge of the lamina origin. The ideal direction of screw angulation is parallel with the posterior arch, in the saggital plane. This entry point was on average 8.8mm from the vertebral artery foramen laterally and 5.8mm from the medial aspect of the lateral mass. Vertical space available for sublaminar screw placement was 3mm or less in 9% of lateral masses. Conclusion: C1 lateral mass screws are best placed beneath the lamina origin, parallel with the arch in the saggital plane using an entrypoint in line with the medial edge of the lamina origin. An entry point under the midpoint of the lamina origin, or passing through the lamina at its attachment to the lateral mass, is likely to damage the vertebral artery in a significant proportion of cases

To introduce a new robot-assisted surgical system for spinal posterior fixation which called TiRobot, based on intraoperative three-dimensional images. TiRobot has three components: the planning and navigation system, optical tracking system and robotic arm system. By combining navigation and robot techniques, TiRobot can guide the screw trajectories for orthopedic surgeries. In this randomised controlled study approved by the Ethics Committee, 40 patients were involved and all has been fully informed and sign the informed consent. 17 patients were treated by free-hand fluoroscopy-guided surgery, and 23 patients were treated by robot-assisted spinal surgery. A total of 190 pedicle screws were implanted. The overall operation times were not different for both groups. None of the screws necessitated re-surgery for revised placement. In the robot-assisted group, assessment of pedicle screw accuracy showed that 102 of 102 screws (100%) were safely placed (<2 mm, category A+B). And mean deviation in entry point was 1.70 +/− 0.83mm, mean deviation in end point was 1.84 +/− 1.04mm. In the conventional freehand group, assessment of pedicle screw accuracy showed that 87 of 88 (98.9%) were safely placed (<2 mm, category A+B), 1 screw fall in category C, mean deviation in entry point was 3.73 +/− 2.28mm, mean deviation in end point was 4.11 +/− 2.31mm. This randomised controlled study verified that robot-assisted pedicle screw placement with real-time navigation is a more accuracy and safer method, and also revealed great clinical potential of robot-assisted surgery in the future

Aims: The accuracy of percutaneous CT-Fluoro navigation is compared with the accuracy of the surface-matching procedure. Methods: 68 transpedicular and transvertebral canals were placed percutaneously in an in vitro. The deviation between probe-position and pre-planed trajectory was measured. Evaluated were the mean deviation of the entry point, the exit point, the transverse trajectory angle deviation and the cranio-caudal trajectory angle deviation. Next the soft tissue was removed and the same procedure was done using CT-based surface matching navigation with a registration root mean square of < 1.0 mm. Results: For CT-Fluoro the mean deviation of the entry point was 1.9 mm ± 0.8 (range 0.1–3.2 mm), the mean exit point deviation on the anterior vertebral cortex was 2.1 mm ± 1.1 (range 0.2–3.8 mm). The measurement after surface matching resulted in 1.5 mm ± 0.6 (range 0.0–3.0 mm) for entry point deviation, 1.9 mm ± 0.9 (range 0.1–5.0 mm) for exit point deviation. Conclusions: There is no statistical significant difference of the accuracy between both procedures (Students T-test). Tissue trauma can be reduced as the posterior surface of the vertebra needs not to be exposed as for contemporary registration methods. This offers new promising aspects in percutaneous and minimally invasive spinal techniques

Introduction. The use of the dynamic hip screw is common practice for the fixation of intertrochanteric fractures of the femur. The success of this procedure requires accurate guide wire placement. This can prove difficult at times and can result in repeated attempts leading to longer operating time, multiple tracks and more importantly greater radiation exposure to both patient and operating staff. We hypothesised that rather than using the standard anterior-posterior projected image (Figure 1) of a proximal femur, rotating the intensifier image (Figure 2) so that the guide wire appears to pass vertically makes it easier to visualise the projected direction of the guide wire. Methods. Fifty Specialist Registrars, thirty participating in the London hip meeting 2009, ten from Oxford and ten from Northern deanery orthopaedic rotations were involved in the study. They were presented with standard AP and rotated images of the femoral neck on paper using 135 degree template to replicate the DHS guide. The participants were asked to mark the entry point on the intertrochanteric area of femur on the image where they would have placed the guide wire. They did this on both standard AP and rotated images aiming for the centre of the head of the femur. Fig. 1 Standard AP image Fig. 2 Rotated image. Results. Thirty-seven Specialist Registrars (74%) were able to accurately mark their entry point on rotated images on their first attempt as compared to eighteen trainees (36%) managing to place it correctly first time on the standard image. Thirteen trainees (26%) were able to mark their entry point correctly on both standard AP and rotated images with equal accuracy. Conclusion. Coren et al. 1 argue that human vision can more easily judge horizontal and vertical lines rather than oblique lines. Thus, rather than use the standard anterior-posterior projected image of the hip, we should routinely rotate the intensifier image so that the guide wire appears to be passing in a vertical direction. By rotating the image (Figure 2) in this way it becomes significantly easier to visualise the projected direction of the guide wire and in doing so ensure its accurate final placement thereby minimising possible complications

Introduction: C1 lateral mass screw fixation offers a powerful alternative biomechanical fixation for upper cervical disorders. The anatomical constraints to this fixation have not been described yet and are essential to ensure avoidance of neurovascular damage. Methods: 50 patients (including 5 patients with rheumatoid arthritis) underwent upper cervical CT scans. Analysis of these CT scans involved use of calibrated scan measurements to identify the midpoint of the posterior lateral mass, the dimensions of the lateral mass, the direction of optimum screw passage, the position of the vertebral foramen at C1 and the ideal entry point for lateral mass screw fixation. Results: The average length of screw within the lateral mass was 20 mm with 13.5mm of screw not in bone, behind the lateral mass, but necessary to allow rod placement posteriorly adjacent to other fixation points. The safest entry point was directly beneath the medial edge of the lamina origin. The ideal direction of screw angulation is parallel with the posterior arch, in the saggital plane. This entrypoint was on average 8.8 mm from the vertebral artery foramen laterally and 5.8 mm from the medial aspect of the lateral mass. Vertical space available for sublaminar screw placement was 3mm or less in 9% of lateral masses. Discussion: C1 lateral mass screws are best placed beneath the lamina origin, parallel with the arch in the saggital plane using an entrypoint in line with the medial edge of the lamina origin. An entry point under the midpoint of the lamina origin, or passing through the lamina at its attachment to the lateral mass, is likely to damage the vertebral artery in a significant proportion of cases

Aim: To assess the impact of three different entry points of the femoral canal preparation with regard to cement mantle thickness in the saggital plane. Methods: We reviewed the literature to find that little has been written on the cement mantle thickness in the saggital plane. We reviewed randomly 60 total hip replacements performed at our institution to discover a common error of a thin cement mantle anteriorly (proximally) and posteriorly (distally) in the saggital plane. We used standard saw-bone preparations of two prosthetic hip systems: Friendly (Lima) and Exeter (Stryker). In each hip system we performed five preparations for each entry point (trochanteric fossa, posterolateral corner and mid point of the cut neck). The only variable was the entry point. Preparation was performed according to the manufacturers’ recommendations. The preparations were x-rayed and cement mantle alignment and thickness were measured on the x-rays. Saggital sections with digital imaging and radial measurements were also performed. Results: The results showed a strong trend towards neutral alignment (antero-posterior (AP) and saggital) and a uniform cement mantle with trochanteric fossa preparation. There was an increasing trend to varus alignment (AP), angled anterior to posterior alignment (saggital) and incomplete cement mantles with postero-lateral corner and mid point of cut neck preparation. Conclusions: We conclude that in cemented femoral replacement, the entry point for canal preparation should be as far lateral and posterior as possible and the trochanteric fossa is the best to achieve neutral alignment and the complete cement mantle

Anterior Cruciate Ligament (ACL) rupture is one of the commonest injuries in sports medicine. However, the rates of the reported graft re-rupture range from 2–10%, leading to around 3000 to 10000 revision ACL reconstructions in United States per annum. Inaccurate tunnel positions are considered to be one of the commonest reasons leading to failure and subsequent revision surgery. Additionally, there remains no consensus of the optimal position for ACL reconstructions. The positions of the bone tunnels in patients receiving ACL reconstruction are traditionally assessed using X-rays. It is well known that conventional X-ray is not a precise tool in assessing tunnel positions. Thus, there is a recent trend in using three-dimensional (3D) CT. However, routine CT carries a major disadvantage in terms of significant radiation hazard. In addition, it is both inconvenient and expensive to use CT as a regular assessment tools during the follow-up. The goal of the present work is to develop a novel 2D-3D registration method using single X-ray image and a surface model. By performing such registration for two post-operative X-rays, we can further calculate the 3D tunnel positions after ACL reconstructions. Our framework consists of five parts: (1) a surface model of the knee, (2) a 2D-3D registration algorithm, (3) a 3D tunnel position calculation, (4) a graphic user interface (GUI), and (5) a semi-transparency rendering. Among them, the crucial part is our 2D-3D registration method that estimates the relative position of the knee model in the imaging coordinate system. Once registered, the 3D position of an ACL tunnel in the knee model is calculated from the imaging geometry. The only interaction required is to mark the ACL tunnels on the X-rays through the GUI. We propose two 2D-3D registration methods. One is a contour-based method that uses pure geometric information. Most methods in this category accomplish the registration by extracting contours in X-rays, establishing their correspondences on the 3D model, and calculating the registration parameters. Unlike these methods, which need point-to-point correspondences, our method optimises the registration parameters in a statistical inference framework without giving or establishing point-to-point correspondences. Due to the use of the statistical inference, our method is robust to the spurs and broken contours that automatically extracted by the contour detector. The second method takes into account both the geometric shape of the object and the intensity property (intensity changes) of the image, where the intensity changes can be detected via image gradients. The use of gradient is based on the interpretation that two images are considered similar, if intensity changes occur at the same locations. The angles between the image gradients and the projected surface normals were used as a distance measure. The summation of the measures for all projected model points gives us the gradient term, which we multiply the contour-based measurement. Multiplication is preferred over addition because addition of the terms would require both terms to be normalised. To evaluate the feasibility of our methods, a simulation study was conducted using Digitally Reconstructed Radiographs (DRR) of a sawbone underwent a single-bundle ACL reconstruction performed by an experienced orthopedic surgeon. The real position of the bone tunnel entry point was obtained using the CT images, which were acquired using a custom-made well-calibrated cone-beam CT. The knee model was built by downsampling and smoothing the high-resolution CT reconstructions. It is important in our experiments to make the model different from the original reconstruction since this simulates the condition in which patient's CT is unavailable. Two DRRs generated from approximately anteroposterior and lateral viewpoints were used. For each DRR, 50 trials of 2D-3D registration were carried out for the femoral part using 50 different initialisations, which were randomly selected from the values independently and uniformly distributed within ±10 degrees and ±10 mm of the ground-truth. Compared with the ground-truth established using the CT images, our single image contour-based method achieved accurate estimations in rotations and in-plane translations, which were (−0.67±1.38, −0.98±0.84, −0.42±0.71) degrees and (0.11±0.26, −0.06±1.20) mm for the anteroposterior image, and (−0.78±0.76, −0.37±0.87, 0.70±0.88) degrees and (−0.14±0.22, 0.31±0.71) mm for the lateral one, respectively. The same experiments were also performed using the second method. However, it did not produce desirable results in our experiments. The tunnel entry point was then calculated using the averaged registration result of our contour-based method. The entry point of the tunnel was obtained with high accuracy of 1.25 mm distance error from the real position of the entry point. For the 2D-3D registration, the estimated off-plane translations showed relatively low accuracy. It is well known that the depth can be difficult to be accurately estimated using one single image. As the result showed, the accuracy in rotations and in-plane translations is more important for ACL tunnel position estimation in our framework. As for the image gradient, it is too sensitive to the small perturbation caused by image noises. A more robust way of integrating the gradient information into our contour-based method is required. We propose a novel approach for estimating the 3D position of bone tunnels in ACL reconstruction using two post-operative X-rays. It was tested in a sawbone study using DRRs. The most significant advantage of our approach is to potentially eliminate the necessity of acquiring a patient's CT. The success in developing and validating the proposed workflow will allow convenient and precise assessment of tunnel positions in ACL reconstruction with minimal risk of radiation hazard

Introduction. Hip resurfacing arthroplasty (HRA) is currently regaining positive attention as a treatment of osteoarthritis in young, active individuals[1]. The procedure is complex and has low tolerance for implant malpositioning [2]. ‘Precision tools', such as imageless navigation and patient specific instruments, have been developed to assist with implant positioning but have not been shown to be fully reliable [3]. The aim of this study is to present and validate the first step of novel quality control tool to verify implant position intra-operatively. We propose that, before reaming of the femoral head, a handheld structured light 3D scanner can be used to assess the orientation and insertion point of femoral guide wire. Methods. Guide wires were placed into the heads of 29 solid foam synthetic femora. A specially designed marker (two orthogonal parallelepipeds attached to a shaft) was inserted into the guide wire holes. Each bone (head, neck and marker) was 3D scanned twice (fig 1). The insertion point and guide wire neck angle were calculated from the marker's parameters. Reference data was acquired with an optical tracking system. The measurements calculated with the 3D scans were compared to the reference ones to evaluate the precision. The comparison of the test retest measurements done with the new method are used to evaluate intra-rater variability. Results. The difference between the entry point measured with the 3D scanner and the reference data was 1.68 mm (SD 2.23 mm). The difference of the measured guide wire axis and the reference axis is 2.44 degrees (SD 2.29). The intra-rater difference was 0.02 mm (SD 0.55mm, ICC 0.9995) for the entry point and 0.20 degrees (SD 0.20, ICC 0.9975) for the guide wire insertion axis. Conclusions. The results of this study indicate that a structured light based 3D scanning technology is accurate in assessing orientation and insertion point of the femoral guide wire during HRA. A small precision bias was identified and further work will need to investigate the cause. Also, inter-rater variability needs to be assessed. This simple verification tool can be used by any hip surgeon and will be most beneficial to those in low-volume centres or in training. It has a potential to be used during teaching and to decrease the learning curve through a self-feedback mechanism. Further studies could use the tool to asses final implant position and focus on other joint replacement procedures requiring high degree of accuracy