Purpose: Dislocation is a short-term complication frequently encountered after implantation of a total hip arthroplasty (THA). Different strategies can be used to limit the influence of technical, particularly surgical, factors. The position of the acetabular element is a key factor, particularly the anteversion angle and the abduction angle. The purpose of this work was to determine the precision, the reproducibility, and the ease of use of a new mechanical guide for insertion of the acetabular cup. Material and methods: After calculating the sample size necessary to achieve 90% statistical power for a 5% type I error, we had five surgeons who regularly implanted THA implant 310 press-fit hip cups on a plastic anatomic model of the pelvis. A new mechanical guide was developed using the constant direction of gravity as the reference frame. We determined the precision of acetabular cup implantation, its reproducibility, and ease of use compared with that of the Müller mechanical guide during in vitro implantation of 310 cups via a posterolateral approach that allowed the usual vision of the operative field. Results: The error of cup anteversion relative to the reference set at 15 was 10.4±5.0 (range 3–21) for the Müller guide and 0.4±0.7 (range 1–3) for the new guide. Cup abduction, relative to the reference set at 45, was −4.7±2.3 (range 7–11) for the Müller guide and 0.3±0.5 (range 0–3) for the new guide. Mean time for positioning the cup was comparable with the two guides (mean 6s for the Müller guide and 5s for the new guide). Discussion: The precision and reproducibility of cup positioning obtained with the new guide are better than those obtained with mechanical guides currently available on the market (p< 0.00001 with the Müller guide). They are more comparable with values found in in vitro studies using computer-assisted surgery techniques. Use of the new guide was also found to be rapid and simple. Conclusion: The excellent results obtained with this new mechanical guide, as assessed in terms of cup position for THA, should be confirmed with in vivo trials

Obtaining consistently an optimal cup orientation in THA is vital to obtain adequate head coverage and maximum impingement free range of motion and thus reduce the incidence of polyethylene wear, cup loosening, and dislocation rates associated with a limited range of motion. It is clear that THA instability, the most frequent cause of early failure, is a complex problem related to a wide range of causes. However cup orientation is one of the surgeon dependant potentially modifiable variables that continue to have an important influence due to the lack of reliable means of assuring an adequate orientation of the components, particularly the cup anteversion. Standard mechanical guides like Muller’s have been shown to be inaccurate and imprecise. Not surprisingly, dislocation is the most frequent short term complication after a THA. Acetabular cup orientation is a key factor determining joint stability and one of the most important ones under the surgeons’ control. An in vitro study was used to determine the precision, reproducibility and ease of use of a new mechanical guide in comparison to a standard mechanical guide Müllers. The new guide (Gravity Assisted Navigation System) consists of a simple to use navigation tool. It uses the constant direction of the force of gravity identified by two bulls’ eye levels providing real time intraoperative augmented reality thus controlling the orientation of the pelvis. Visualisation of the guide from a single perspective is enough to determine in real time, the orientation of the cup in abduction and anteversion. By using anatomic repairs within the pelvis its flexion/extension is taken into consideration. As part of an invitro study, 310 press-fit acetabular cups were impacted into a plastic model of a pelvis by 5 surgeons (Power 90%, Type I error 5%), The orientation obtained was measured with respect to a fixed reference of 15° of anteversion and 45° of abduction. Results: an average of 10.4° anteversion ,(Range 3°to 21°, Standard of Deviation 5.0°) for Müller s guide and of 0.4° anteversion (Range 1° to 3°, Standard of Deviation 0.7°) for the new guide and an average of −4.7° abduction (Range 7° to −11°, Standard of Deviation 2.3°) for Müllers guide and 0.3° abduction (Range 0° to 3°, Standard of Deviation 0.5°) for the new guide. The average time required for the orientation of the cups was similar with both guides. (6 seconds for Mullers guide and 5 seconds for the new guide) The precision and reproducibility of the cup orientation obtained with the new guide were significantly better than those obtained with Müllers guide (p< 0.00001). The results obtained with with the new mechanical guide are encouraging. The in vitro results are encouraging, the high precision and accuracy are comparable to results obtained by computer assisted navigation systems in similar studies

Purpose: The increasing number of ACL reconstructions has led to the introduction of new techniques irrespective of the fact optimal tunnel angle placement has yet to be established. Improper tunnel angle placement is associated with a variety of complications including graft failure. The purpose of this retrospective study was to compare the reliability of tibial tunnel angles produced by two experienced surgeons using a free hand method or mechanical guide (HowellTM 65° Tibial Guide). Method: Tibial tunnel angles in the coronal and sagittal planes were determined from anteroposterior and lateral radiographs, respectively, taken at 2 to 6 months postoperatively. Fifty-two sets of digital radiographs were analyzed (free hand = 28, mechanical = 24) with the knee in full extension 100 cm from the beam source. Tunnel angle measurements were calculated using NIH ImageJ software. Each angle was measured by two investigators on three separate occasions with minimum 7 days between each analysis. Results: There was a significant difference (p< 0.05) in tibial tunnel angle placement between the mechanical guide (64.76 ± 5.88) and free hand (61.11 ± 5.04) group in the coronal plane. No significant difference in tibial tunnel placement in the sagittal plane was detected (mechanical guide =73.63 ± 7.69, free hand = 73.51 ± 6.68). Intra-rater and Inter-rater reliability for measurements in the sagittal (ICC = 0.809; 0.733) and coronal (ICC = 0.69; 0.812) plane ranged from high (> 0.75) to moderate (0.75–0.40), respectively. Conclusion: Tibial tunnel angles in the coronal plane produced with a mechanical guide are more accurate than those drilled free hand when the intended angle of placement is 65°. The method used to measure tibial angles in this study was reliable within and between investigators. Further research will be conducted to investigate the correlation between tunnel angle placement and patient outcome measures

Introduction. Acetabular component orientation is an important determinant of outcome following total hip arthroplasty (THA). Although surgeons aim to achieve optimal cup orientation, many studies demonstrate their inability to consistently achieve this. Factors that contribute are pelvic orientation and the surgeon's ability to correctly orient the cup at implantation. The goal of this study was to determine the accuracy with which surgeons can achieve cup orientation angles. Methods. In this in vitro study using a calibrated left and right sawbone hemipelvis model, participants (n=10) were asked to place a cup mounted on its introducer giving different targets. Measurements of cup orientation were made using a stereophotogrammetry protocol to measure radiographic inclination and operative anteversion (OA). A digital inclinometer was used to measure the intra-operative inclination (IOI) which is the angle of the cup introducer relative to the floor. First, the participant stated his or her preferred IOI and OA and positioned the cup accordingly. Second, the participant had to position the cup parallel to the anteversion of the transverse acetabular ligament (TAL). Third, the participant had to position the cup at IOI angles of 35°, 40° and 45°. Fourth, the participant used the mechanical alignment guide (45° of IOI and 30° of OA) to orient the cup. Each task was analysed separately and subgroup analysis included left versus right side and hip surgeons versus non-hip surgeons. Results. For the first task, hip surgeons preferred smaller IOI and larger OA than non-hip surgeons, but there was no significant difference in accuracy between both groups. When aiming for TAL, both surgeon groups performed similar, but accuracy on the non-dominant side was significantly better compared with the dominant side (mean deviation 0.6° SD 2.4 versus −2.6° SD 2.3) (p=0.004). When aiming for a specific IOI target of 35°, 40° or 45°, non-hip surgeons outperformed hip surgeons (mean deviation form target IOI 1.9° SD 2.7 versus −3.1° SD 3.8) (p<0.0001) with less variance (p=0.03). Contrary to version, accuracy on the dominant side was significantly better compared with the non-dominant side (mean deviation −0.4° SD 3.4 versus −2.1° SD 4.8). When using a mechanical guide, surgeons performed similar (0.6° SD 1.2 versus −0.4° SD 2.1 for inclination p=0.11 and −0.5° SD 2.6 versus −1.8° SD 3.3 for version p=0.22) and these values did not differ significantly from the actual IOI and OA of the mechanical guide. When using a mechanical guide, there was no difference in accuracy between the dominant and non-dominant side. Conclusion. There was no difference in accuracy between hip surgeons and non-hip surgeons when they aimed for their preferred IOI and OA or used a mechanical guide. When aiming for a specific IOI target, non-hip surgeons outperformed hip surgeons. Hip surgeons overestimate IOI and underestimate OA, presumably because this helps to achieve the desired radiographic cup orientation. Regarding accuracy, the non-dominant side was better for version and the dominant side for inclination. When aiming for a specific IOI and OA target, using a mechanical guide is significantly better than freehand cup orientation

Extracellular matrix (ECM) mechanical cues guide healing in tendons. Yet, the molecular mechanisms orchestrating the healing processes remain elusive. Appropriate tissue tension is essential for tendon homeostasis and tissue health. By mapping the attainment of tensional homeostasis, we aim to understand how ECM tension regulates healing. We hypothesize that diseased tendon returns to homeostasis only after the cells reach a mechanically gated exit from wound healing. We engineered a 3D mechano-culture system to create tendon-like constructs by embedding patient-derived tendon cells into a collagen I hydrogel. Casting the hydrogel between posts anchored in silicone allowed adjusting the post stiffness. Under this static mechanical stimulation, cells remodel the (unorganized) collagen representing wound healing mechanisms. We quantified tissue-level forces using post deflection measurements. Secreted ECM was visualized by metabolic labelling with non-canonical amino acids, click chemistry and confocal microscopy. We blocked cell-mediated actin-myosin contractility using a ROCK inhibitor (Y27632) to explore the involvement of the Rho/ROCK pathway in tension regulation. Tissue tension forces reached the same homeostatic level at day 21 independent of post compliance (p = 0.9456). While minimal matrix was synthesized in early phases of tissue formation (d3-d5), cell-deposited ECM was present in later stages (d7-d9). More ECM was deposited by tendon constructs cultured on compliant (1Nm) compared to rigid posts (p = 0.0017). Matrix synthesized by constructs cultured on compliant posts was less aligned (greater fiber dispersion, p = 0.0021). ROCK inhibition significantly decreased tissue-level tensional forces (p < 0.0001). Our results indicate that tendon cells balance matrix remodeling and synthesis during tissue repair to reach an intrinsically defined “mechanostat setpoint” guiding tension-mediated exit from wound healing towards homeostasis. We are identifying specific molecular mechanosensors governing tension-regulated healing in tendon and investigate the Rho/ROCK system as their possible downstream pathway

Restoration of proper alignment is one of the principle goals of TKA. Various methods are popular, including intramedullary (IM) and extramedullary (EM) mechanical guides, and recently computer assisted navigation (CAS). In addition, minimally invasive surgery has added an extra level of complexity to achieving satisfactory alignment. The purpose of this study was to determine the effect of approach (standard arthrotomy vs MIS) and alignment technique (Mechanical vs CAS) upon component alignment in TKA. Methods. Three consecutive cohorts of patients were included: Group I--Standard arthrotomy with Mechanical guides; Group II-MIS approach with Mechanical guides; Group III-MIS approach with CAS. A single surgeon performed the Standard Mechanical cohort, and a second surgeon performed all surgeries in the other two cohorts. For the mechanical groups, IM femoral and EM tibial guides were used. For CAS, the Orthosoft system was used. All components were NexGen (Zimmer) Postoperative x-rays were used to measure component alignment relative to the IM axes, including femoral valgus and flexion, and tibial varus and slope, and patellar tilt. In addition, joint line position was measured. Students’ t-test was used to determine level of significance. Results. For Groups I, II and III, there were 41, 38 and 39 patients, respectively. For femoral alignment in the coronal plane, results were 4.83+4.29 degrees, 3.82+2.72 degrees, and 3.36+2.49 degrees, respectively. Femoral flexion was 2.93+2.82 degrees, 3.18+2.93 degrees, and 2.46+2.79 degrees, respectively. Tibial alignment was 0.44+3.98 degrees of varus, 1.00+2.83 degrees of valgus, and 0.95+2.58 degrees of varus, respectively. Slope was 6.78+3.23 degrees, 3.23+3.21 degrees, and 3.93+2.85 degrees, respectively. Patellar tilt was 2.15+3.51 degrees lateral, 1.73+2.67 degres lateral, and 1.03+2.28 degrees lateral, respectively. The joint line was raised 1.18+3.54 mm and 0.05+4.92 mm in Groups I and III, respectively, and lowered 0.33+4.78 mm in Group II. There were no statistically significant differences in any measurement between any groups. Discussion. Satisfactory alignment can be achieved with either mechanical guides or navigation systems. MIS approaches do not worsen alignment with either alignment methodology. Whether having fewer outliers translates into improved clinical outcomes remains to be seen. More importantly, CAS provides an intraoperative tool that may allow more accurate reproduction of a customized plan for an individual, rather than simply attempting to achieve the “mean” for a population. Again, the value of achieving such a goal is unknown since the threshold for improvement with off-the-shelf knee components may have already been maximised

Background. The current orthopaedic literature demonstrates a clear relationship between acetabular component positioning, polyethylene wear and risk of dislocation following Total Hip Arthroplasty (THA). Problems with edge loading, stripe wear and squeaking are also associated with higher acetabular inclination angles, particularly in hard-on-hard bearing implants. The important parameters of acetabular component positioning are depth, height, version and inclination. Acetabular component depth, height and version can be controlled with intra-operative reference to the transverse acetabular ligament. Control of acetabular component inclination, particularly in the lateral decubitus position, is more difficult and remains a challenge for the Orthopaedic Surgeon. Lewinnek et al described a ‘safe zone’ of acetabular component orientation: Radiological acetabular inclination of 40 ± 10° and radiological anteversion of 15 ± 10°. Accurate implantation of the acetabular component within the ‘safe zone’ of radiological inclination is dependent on operative inclination, operative version and pelvic position. Traditionally during surgery, the acetabular component has been inserted with an operative inclination of 45°. This assumes that patient positioning is correct and does not take into account the impact of operative anteversion or patient malpositioning. However, precise patient positioning in order to orientate acetabular components using this method cannot always be relied upon. Hill et al demonstrated a mean 6.9° difference between photographically simulated radiological inclination and the post-operative radiological inclination. The most likely explanation was felt to be adduction of the uppermost hemipelvis in the lateral decubitus position. The study changed the practice of the senior author, with target operative inclination now 35° rather than 40° as before, aiming to achieve a post-operative radiological inclination of 42° ± 5°. Aim. To determine which of the following three techniques of acetabular component implantation most accurately obtains a desired operative inclination of 35 degrees:. Freehand. Modified (35°) Mechanical Alignment Guide, or. Digital inclinometer assisted. Methods. 270 patients undergoing primary uncemented THA were randomised to one of the three methods of acetabular component implantation. Target operative inclination for all three techniques was 35°. Operative inclination was measured intra-operatively using both a digital inclinometer and stereophotogrammetric system. For both the freehand and Mechanical Alignment Guide implantation techniques, the surgeon was blinded to intra-operative digital inclinometer readings. Results. The freehand implantation technique had an operative inclination range of 25.2 – 43.2° (Mean 32.9°, SD 2.90°). The modified (35°) Mechanical Alignment Guide implantation technique had an operative inclination range of 29.3 – 39.3° (Mean 33.7°, SD 1.89°). The digital inclinometer assisted technique had an operative inclination range of 27.5 – 37.5° (Mean 34.0°, SD 1.57°). Mean unsigned deviation from target 35° operative inclination was 2.92° (SD 2.03) for the freehand implantation technique, 1.83° (SD 1.41) for the modified (35°) Mechanical Alignment Guide implantation technique and 1.28° (SD 1.33) for the digital inclinometer assisted technique. Conclusions. When aiming for 35° of operative inclination, the digital inclinometer technique appears more accurate than either the freehand or Mechanical Alignment Guide techniques. In order to improve accuracy of acetabular component orientation during Total Hip Arthroplasty, the surgeon should consider using such a technique

Minimally invasive total hip replacement surgery not only decreases the number of visual cues necessary for proper acetabular component position, the small incision makes it technically more difficult to use traditional mechanical alignment guides. Furthermore, traditional mechanical guides have been shown to be unable to accurately predict component position as determined by intraoperative computer measurements.[ 1,2 ] Computer assisted intraoperative navigation can enable minimally invasive surgery by giving the surgeon immediate intra-operative feedback of actual component position. We wished to compare the intraoperative computer determined measurement of acetabular inclination with the postoperative radiographic measurement of inclination in order to validate the results of the computer assisted measurements in the clinical setting. To determine whether computer assisted navigation of the acetabular component allows the surgeon to accurately place the prosthesis in minimally invasive hip replacement and to compare the results of intraoperative navigation with the postoperative radiograph. 42 consecutive patients underwent a minimally invasive posterior approach for total hip arthroplasty with the assistance of CT based intraoperative navigation with the BrainLAB VectorVision software. Preoperative surgical planning was performed after acquisition of a CT scan. All components were templated to be placed in 45 degrees of inclination and 25 degrees of anteversion. Intraoperatively, cementless acetabular components were aligned with the computer navigation at these values prior to implant impaction. Because of the press fit nature and limited soft tissue exposure, many components would shift during impaction. Final component position was then verified and values recorded by detecting points on the acetabular surface. If the prosthesis was felt to be in an acceptable position, no attempt was made to modify component position to the predetermined values in order to avoid potentially compromising component fixation. Postoperative supine AP pelvis radiography was then used to determine final inclination. Measurements were made by drawing a line perpendicular to the acetabular teardrop and parallel to the acetabular component and measured with a standard goniometer. These data were then placed in an SPSS database and analyzed by an independent statistician. Assessing acetabular component position in routine total hip arthroplasty has been shown to be unreliable even with experienced surgeons with mechanical alignment guides. [1,3] In minimally invasive total hip arthroplasty, routine visual cues are limited and mechanical instruments are difficult to place in the small operative wounds making an already difficult task even more difficult. CT based image guided surgery can has been shown to improve the acetabular component position intraoperatively 2. However, postoperative validation studies comparing the intraoperative computer assessment with the postoperative radiographic measurement are scarce. [ 2 ] In this consecutive series, which represents the author’s first experience with this technology, several conclusions can be made. First, the act of impacting a solid, porous coated, hemispherical cementless acetabular component in minimally invasive hip surgery often leads to a final component position different from the intended position. Second, computer generated determination of implant position is reliable but care must be taken to make sure the reference arrays do not lose fixation during the procedure or spurious results can occur. Third, routine AP pelvis radiographic measurements are not accurate enough to determine whether the computer determined values are accurate. In spite of these measurement inaccuracies, the computer determined results and the radiographic results were within 10 degress 95 % of the time which is far more accurate than results obtained with mechanical alignment tools 3. Finally, further validation studies need to be done with postoperative CT scanning to determine the accuracy of the intraoperative computerized measurements and determine the measurement errors inherent in the clinical setting. Given these limitations, computer assisted navigation improves the accuracy and reliability of acetabular component position over traditional mechanical instruments and can be utilized in minimally invasive hip surgery to assist in the appropriate placement of the acetabular prosthesis

Introduction. Operative inclination (OI) is defined as the angle between the acetabular axis and the sagittal plane. With the patient in the true lateral decubitus position, this corresponds to the angle formed between the handle of the acetabular component inserter and the theatre floor intra-operatively. Patients/Materials & Methods. The primary study aim was to determine which method of acetabular component insertion most accurately allows the surgeon to obtain a target OI of 35o. 270 consecutive patients undergoing cementless THA were randomised to one of three possible methods for acetabular component implantation:. 1. Freehand,. 2. 35o mechanical alignment guide (MAG), or. 3. Digital inclinometer assisted. Two surgeons participated. Target OI was 35o in all cases. OI was measured using a digital inclinometer. For the freehand and MAG cases, the surgeon was blinded to inclinometer readings intra-operatively. Results. Freehand: OI 25.2 – 43.2o. Mean deviation from target 2.92o. 35o MAG: OI 29.3 – 39.3o. Mean deviation from target 1.83o. Inclinometer assisted: OI 27.5 – 37.5o. Mean deviation from target 1.28o. Overall, when comparing mean deviation from target OI, a statistically significant difference between both the Freehand/Inclinometer group and Freehand/MAG group was demonstrated (p<0.001). A statistically significant difference between the Inclinometer/MAG groups was also demonstrated (p<0.023). Discussion. Both the 35o MAG and digital inclinometer assisted methods provided a considerably narrower OI range when compared to the freehand method. Though the range was similar for both the 35o MAG and digital inclinometer assisted methods, the SD was smaller in the inclinometer assisted group. Conclusion. The novel method of using a digital inclinometer to control operative inclination appears to be more accurate than both the freehand and mechanical alignment guide methods and may help further optimise acetabular component orientation

INTRODUCTION. Acetabular cup malpositioning has been implicated in instability and wear-related complications after total hip arthroplasty. Although computer navigation and robotic assistance have been shown to improve the precision of implant placement, most surgeons use mechanical and visual guides to place acetabular components. Authors have shown that, when using a bean bag positioner, mechanical guides are misleading as they are unable to account for the variability in pelvic orientation during positioning and surgery. However, more rigid patient positioning devices may allow for more accurate free hand cup placement. To our knowledge, no study has assessed the ability of rigid devices to afford surgeons with ideal pelvic positioning throughout surgery. The purpose of this study is to utilize robotic-arm assisted computer navigation to assess the reliability of pelvic position in total hip arthroplasty performed on patients positioned with rigid positioning devices. METHODS. 100 hips (94 patients) prospectively underwent total hip Makoplasty in the lateral decubitus position from the posterior approach; 77 stabilized by universal lateral positioner, and 23 by peg board. After dislocation but prior to reaming, one fellowship trained arthroplasty surgeon manually placed the robotic arm parallel to both the longitudinal axis of the patient and the horizontal surface of the operating table, which, if the pelvis were oriented perfectly, would represent 0 degrees of anteversion and 0 degrees of inclination. The CT-templated computer software then generated true values of this perceived zero degrees of anteversion and inclination based on the position of the robot arm registered to a preoperative pelvic CT. Therefore, variations in pelvic positioning are represented by these robotic navigation generated values. To assure the accuracy of robotic measurements, cup anteversion and inclination at times of impaction were recorded and compared to those calculated via the trigonometric ellipse method of Lewinnek on standardized 3 months postoperative X-rays. RESULTS. Mean alteration in anteversion and inclination values were 1.7 degrees (absolute value 5.3 degrees, range −20 – 20 degrees) and 1.6 degrees (absolute value 2.6 degrees, range −8 – 10 degrees) respectively. 22% of anteversion values were altered by >10 degrees; 41% by > 5 degrees. There was no difference between positioners (p=0.36) and regression analysis revealed that anteversion differences were correlated with BMI (p=0.02). Robotic navigation acetabular cup anteversion (mean 21.8 degrees) was not different from postoperative X-ray anteversion (mean 21.9 degrees)(p=0.50), nor was robotic navigation acetabular cup inclination (mean 40.6 degrees) different from postoperative X-ray inclination (mean 40.5 degrees)(p=0.34). DISCUSSION AND CONCLUSION. Rigid pelvic positioning devices present 5 to 20 degrees of variability in acetabular cup orientation, particularly with regards to anteversion. Compounding this with 20 degree safe zones and prior author demonstrations that human error is prone to 10 degrees of anteversion inaccuracy in a fixed pelvis model, there is a clear need to pay particular attention to anatomic landmarks or computer assisted techniques to assure accurate acetabular cup positioning. Patient positioning by itself should not be trusted

Introduction:. One of the primary goals in total knee arthroplasty (TKA) is restoration of the mechanical alignment. The accuracy of conventional mechanical alignment guides and computer-assisted navigation systems has been extensively studied. The purpose of this study is to assess the accuracy of a hand-held accelerometer-based navigation system for TKA. Methods:. Fifty three patients undergoing TKA utilizing the KneeAlign system (OrthAlign Inc, Aliso Viejo, CA) (Figure 1) were performed by two surgeons. Intraoperative data including tourniquet time, device assembly time, and resection times were recorded. Target alignment goals were 0° femoral, tibial, and overall mechanical coronal alignment and 3° femoral flexion and posterior tibial slope. Coronal/sagittal alignment of the implant and the mechanical axis were measured by two independent observers on full length (54 inch) postoperative hip to ankle radiographs. Results:. Average femoral coronal alignment was 0.29° varus ± 2.2° with 13% of patients exceeding 3° of varus/valgus. Average tibial coronal alignment was 0.25° valgus ± 1.4° with 4% of patients exceeding 3° of varus/valgus. Average femoral flexion angle was 87.2° and the average tibial posterior slope was 2.8° ± 1.8 °. Average postoperative mechanical axis was 0.2° varus ± 2.1°with 13% of patients exceeding 3° of varus/valgus (Figure 2). The average time to completion of femoral and tibial resection was 4.8 and 4.6 minutes, respectively, with an overall tourniquet time of 62 minutes. Conclusion:. The KneeAlign system was accurate for reestablishing the mechanical axis and the femoral and tibial component alignment in TKA without increasing surgical time. Accuracy was better for tibial than femoral resection, but overall superior to mechanical alignment guides and comparable to computer-assisted navigation

Introduction. In total hip arthroplasty (THA), a high radiographic inclination angle (RI) of the acetabular component has been linked to an increased dislocation rate, liner fracture, and increased wear. In contrast to version, we have more proven boundaries when it comes to a safe zone for angles of RI. Although intuitively it seems easier to achieve a target RI, most studies demonstrate a lack of accuracy and the trend towards a high RI with all surgical approaches when using a freehand technique or a mechanical guide. This is due to pelvic motion during surgery, which can be highly variable. The current study had two primary aims, each with a different primary outcome. The first aim was to determine how accurate a surgeon could obtain the target operative inclination (OI) during THA when using a cementless cup using a digital protractor. The second aim was to determine how accurate a surgeon can estimate the target OI to obtain a RI of 40° based on the patient's hip circumference as demonstrated in a previous study. Methods. In this prospective study, we included 200 consecutive patients undergoing uncemented primary THA in the lateral decubitus position using a posterior approach. Preoperatively, the surgeon determined the target OI based on the patient's hip circumference (22.5°, 25°, 27.5° or 30°). Intraoperatively, the effective OI was measured with the aid of a digital inclinometer after seating of the acetabular component. Six weeks postoperatively anteroposterior pelvic radiographs were made and two evaluators, blinded to the effective OI, measured the RI of the acetabular component. The safe zone for inclination was defined as 30°-45° of inclination. Results. The mean difference between the target OI and the effective OI of the acetabular component was −0.7° SD 1.4 (95% CI −0.9° to −0.5°). The difference between the target and effective OI was less than 1° in 108 patients (54%), less than 2° in 160 patients (80%) and less than 3° in 186 patients (93%). In 14 patients (7%) the difference was 3°-5°. The mean RI was 37.9° SD 4.7 (95% CI 37.2° to 38.5°). The mean difference between the RI and effective OI was 11.5° SD 4.7 (95% CI 10.8° to 12.1°). Overall, 188 cups (94%) were within the inclination safe zone. When analysing the RI outliers, 1 could have be avoided if a better target OI was chosen and 2 could have been avoided if the difference between the target and effective OI would have been smaller. For the remaining 9 outliers (75%) the difference between the RI and effective OI was in the upper and lower 7. th. percentile, indicating more or less than average motion of the pelvis in these patients. Discussion and Conclusions. When using a digital protractor, the mean difference between the target OI and the effective OI of the acetabular component was less than 3° in 93% and less than 5° in all patients. The use of a digital protractor allows surgeons to accurately implant the acetabular component in the desired OI in a cheap and easy way. By adjusting the target OI based on the patient's hip circumference, 94% of the acetabular components were placed within an inclination safe zone of 30°-45°. Most outliers were caused by more of less than average intraoperative pelvic motion

The disadvantages of sawing for precise bone cuts are well known: untrue cuts, heat and metal wear. The main limiting factors of available milling devices are the difficult handling and high costs, especially if the devices are based on a robot. Supported by clinical users and mechanical engineers a milling concept adopted from machining has been realised in order to overcome this limitations. The „All-in-One Milling-Tool“ achieves the same precision of a robot by a mechanically guided milling resection far below the necessary investment for a robot. Three methods are provided for the alignment of the resection planes and will be discussed: intramedullary adjustment, 3D CT-based planning and intramedullar performance as well as the performance under control by navigation. All versions are based on a handheld resection and guarantee a visual and haptical feedback for the surgeon. The use of navigation has the advantage of the accurate transfer of the 3D plan into the OR, the interactive facilitated alignment und resection steps and the documentation of planned and actual implant position

Introduction: Navigation increases the precision and reproducibility of reconstruction in THR. It is important for the surgeon to be able to trust the reproducibility of the navigator and that navigated surgery should produce better results than those obtained by the surgeon by himself. The aim of this study is to determine the reproducibility and trustworthiness of a navigation system for acetabular reconstruction and to compare the precision of the navigator with that of the surgeon. Materials and methods: A total of 101 THRs were carried out in 99 patients using image-free navigation. The precision and reproducibility of the navigator were measured with 30 postoperative CT scans. The blind estimates of the surgeons for inclination and anteversion were compared to the values of the navigator; the navigator was as accurate as the surgeon in 101 cases. Results: The precision of the navigator for inclination was 4.4° with a reproducibility of 0.03 and for ante-version it was 4.1° with a reproducibility of 0.73. The precision of experienced surgeons for inclination was 11.5° and 12.3° for anteversion (less experienced surgeons had a precision for inclination of 13.1° and for anteversion of 13.9°). Conclusions: Computer accuracy for the real value of a CT scan is always within 5°. The estimations of the surgeons with mechanical guides, experience and good judgment are about 12 degrees that of the navigation system. However the percentage of values 5° higher than the desired levels in experienced surgeons is seen in about 30% of cases (in less experienced surgeons, in about 50%). The computer can eliminate acetabular malposition to within about 5 degrees for desired values and in this way improve stability and wear

The disadvantages of sawing for precise bone cuts are well known: untrue cuts, heat and metal wear. The main limiting factors of available milling devices are the difficult handling and high costs, especially if the devices are based on a robot. Supported by clinical users and mechanical engineers a milling concept adopted from industrial machining has been realised in order to overcome this limitations. The “All-in-One Milling-Tool” achieves the same precision of a robot by a mechanically guided milling resection far below the necessary investment for a robot. Once fixed at the femur, the device allows all femural and tibial resections. Three methods are provided for the alignment of the resection planes and will be discussed: intramedullary adjustment, 3D CT-based planning and intramedullar performance as well as the performance under navigation control. All versions are based on a handheld resection and guarantee a visual and haptical feedback for the surgeon. The use of navigation has the advantage of the accurate transfer of the 3D plan into the OR, the interactive guided and facilitated alignment und resection steps and the documentation of planned and actual implant position

Purpose: The purpose of this clinical trial was to investigate the accuracy of a novel method for computer-assisted distal radius osteotomy, in which computer-generated patient-specific plastic guides were used for intra-operative guidance. Our hypothesis was that these guides combine the accuracy and precision of computer-assisted techniques with the ease of use of mechanical guides. Method: In a consecutive series of 9 patients we tested the accuracy of the proposed method. Prior to surgery, CT scans were obtained of both radii and ulnae in neutral rotation. Three-dimensional virtual models for both the affected and unaffected radius and ulna were created. The models of the unaffected radius and ulna were reflected to serve as a template for the correction. Custom-made software was used to plan the correction. The locations of the distal and proximal drill holes for the plate were saved and the locations of the distal holes before the osteotomy were determined. The design of a patient-specific instrument guide was calculated, into which a mirror image of intra-operative accessible bone structure of the distal radius was integrated. This allowed for unique positioning of the guide intra-operatively. For each planned drill location a guidance hole was incorporated into the guide. A plastic model of the guide was created using a rapid prototyping machine. Intra-operatively, a conventional incision was made and the guide was positioned on the distal end of the radius. The surgeon drilled the holes for the plate screws into the intact radius. The guide was removed and the surgeon performed the osteotomy using the conventional technique and shaved the bone from the distal radius fragment to accommodate the plate. Using the pre-drilled holes the plate was affixed to the distal radius fragment. The distal fragment was reduced until the proximal screw holes in the plate aligned with the pilot holes in the bone. To analyze the accuracy of the intra-operative procedure we compared the post-operative alignment of the radius with the planned alignment. A lateral and an A/P digitally reconstructed radiograph (DRR) of the plan were calculated. These DRRs were used to evaluate the radial inclination, the volar tilt and the ulnar variance of the planned alignment. Post-operative lateral and A/P X-Rays were used to determine the same three post-operative radiographic indices. The post-operative values were compared with the planned values. Results: We found an average deviation for the radial inclination of 0.5°(StDev 1.8), for the volar tilt of 0.7°(StDev 2.3), and for the ulnar variance of 0.8mm (StDev 1.9). Conclusion: These results show that the computer-generated instrument guides accurately achieved the planned alignment. The guides were easy to integrate into the surgical workflow and eliminated the need for intra-operative fluoroscopy for guidance of the procedure

Introduction Malpositioning of cup and stem in total hip replacement can result in significant clinical problems such as dislocation, impingement, limited range of motion and increased polyethylene wear. The use of mechanical alignment guides for correct cup positioning has been shown to result in large variations of cup inclination and version. Methods Bilateral total hip replacements were performed in twelve human cadavers. While in each cadaver the operation on one side was performed with the aid of a non image based hip navigation system, the cup positioning at the contralateral hip was controlled by use of a conventional mechanical alignment guide. Post-operative cup position relative to the pelvic reference plane was assessed in both groups by the use of a 3D digitizing arm. Results By aiming for 45° inclination and 20° anteversion for cup position the median inclination was assessed as 45.5° for the navigated group and 41.8° for the control group. Median anteversion in the navigated group was calculated as 21.9° and 24.6° for the control group. The 90 percentile showed a much wider range for the control group (36.1° to 51.8° inclination, 15° to 33.5° anteversion) than for the navigated group (43.9° to 48.2° inclination, 18.3 ° to 25.4° anteversion). Conclusions The cadaver study demonstrates that computer assisted cup positioning using a non-image based hip navigation system allowed a more precise placement of the acetabular component in the surgeon’s desired orientation with less variance than in the control group. In relation to the conduct of this study, one or more the authors have received, or are likely to receive direct material benefits

Computer-assisted techniques are developed to optimise the positioning of acetabular cups in total hip replacement. However, ordinary guiding devices are still most commonly used. The aim of this study was to evaluate the accuracy when using a simple mechanical guiding device. 30 patients were operated by an experienced hip surgeon. A lateral position and a lateral approach were used. An un cemented press fit cup (Trilogy AB) was inserted using the guiding device for this type of pros-thesis, aiming 45 degrees abduction and 20 degrees ante-version. Radiological investigations were performed one week and three months postoperatively. Frontal views of the pelvis and of the operated hip were obtained. After scanning the contour of the opening of the acetabular prosthesis was identified and digitised using an edge detecting technique. The axes of the ellipsis of the acetabular opening served for calculation of the version of the cup. A lateral view clarified whether the cup was ante- or retroverted. The abduction related to the teardrop-line was measured on the scanned pelvic radiograph. One week postoperatively mean abduction was 50 degrees (37–62), SD 5 degrees. Mean anteversion measured on the pelvic view was 9 degrees (2–23), SD 5 degrees, compared to 11 degrees (4–24), SD 5 degrees, on the frontal view of the hip joint 50 per cent of the cups showed a deviation of more than 10 degrees from the aimed anteversion.. At average the anteversion was 2 degrees lower when measured on the pelvic view compared to that measured on the AP-view of the hip. There were no significant differences between the measurements at one week and three months. The anteversion of uncemented press fit acetabular components tends to be lower than intended when using a simple guiding device. The risk of an unacceptable abduction seems negligible. The inaccuracy in acetabular positioning may be due to inadequate positioning of the pelvis or inaccurate insertion technique

The purpose of this research is to propose CT-free cup orientator using tilt sensors without expensive point tracking devices in total hip replacement. In the case of using a mechanical guide, the accuracy of cup orientation can be sacrificed because of change of the patient’s posture during procedure. Several navigation systems have been introduced to secure an accurate position and orientation of the implant in THR. These systems are expensive and have some weakness due to possible interference inoptical measurement. Our orientator employs a T-bar shaped gauge and economic tilt sensors to secure a fairly orientation of acetabular cup inTHR. The T-bar gauge having three feet with adjustable distance is designed to obtain the anatomical landmarks concurrently. Each foot is placed on the anatomical landamark of the sawbone. The gauge has its own tilt sensor to identifiy the tilt angle of the guage using AD input board. Similary, the cup positioning tool and dynamic reference base (DRB) have their own tilt sensors. The experimental procedures of CT-free cup orientator are done as follows:. Place the T-bar gauge in right place on the pelvis by setting three feet on the ASIS and pubic. Attach DRB to pelvis and align its orientation parallel to the T-bargauge. Align the tilt sensor of the cup positioner parallel to DRB. We define errors as difference between experimental data and ground truth obtained by Micro-Scribe (Immersion Inc.) Errors of the cup in abduction and anteversion were 1.2 and 1.0 degrees respectively when the test is performed on a sawbone. We analyzed the causes of error to improve the accuracy of our cup orientator. Measuring landmarks and aligning three tilt sensors seemed to cause some errors. Base on this study, we expect to make an experiment on cadaver

Introduction: The correct position of the knee arthroplasty components is associated with a better result of the prosthesis. In the tibial component, both intramedullar and extramedullar instrumentations have been used for its fiability, but in the femoral component intramedullar guides are more precise than extramedullar ones. The use of the intramedullar guide for the femoral component is not always possible, because a significant deformity of the femoral shaft or when a intramedullar device has been implanted in the femur. We have studied the alineation of the components of computer assisted total knee arthroplasties in a group of patients with femoral deformities or implants. Material and methods: We have used the surgical navigator Stryker-Howmedica for the implantation of a knee arthroplasty in a group of 10 patients in which a endomedullar femoral guide can not be used for femoral shaft severe deformities (6 cases): Paget disease (1 case), previous femoral osteomyelitis (2 cases) or previous femoral fractures (3 cases), or a shaft device was in the femoral shaft (4 cases): long hip femoral stem (3 cases) or a femoral nail (1 case) . We have studied the alineation of femoral and tibial components with a whole-leg X-ray and Computer Tomography. Results: All the femoral and tibial components have been implanted in a good position (90 +/– 2 degrees in the A-P plane and a femorotibial axe 180 +/– 3 degrees. The alineation in the sagital and axial planes have been inside the desired values in all cases also. Discussion: It is generally accepted than intramedullary guides for the femoral component is the gold standard in arthroplasty of the knee. In the last years, the development of computer assisted systems has allowed to obtain femoral and tibial cuts referred to the mechanical axes of the bone, without using mechanical guides for the alineation. In some studies these navigation systems are better than mechanical instruments in terms of alineation of the components in cases without great deformities. In this study, with some cases with severe femoral shaft deformities or with some intramedullary devices that does not allow the use of intramedullary femoral guides, we think that the indication to use a surgical navigator should be nearly absolute