Background. The surgical management of musculoskeletal tumours is a challenging problem, particularly in pelvic and diaphyseal tumour resection where accurate determination of bony transection points is extremely important to optimise oncologic, functional and reconstructive options. The use of computer assisted navigation in these cases could improve surgical precision. Materials and methods. We resected musculoskeletal tumours in fifteen patients using commercially available computer navigation software (Orthomap 3D). Results. Of the eight pelvic tumours, three underwent biological reconstruction with extra corporeal irradiation, three endoprosthetic replacement (EPR) and two required no bony reconstruction. Four diaphyseal tumours had biological reconstruction. Two patients with proximal femoral sarcoma underwent extra-articular resection and EPR. One soft tissue sarcoma of the adductor compartment involving the femur was resected with EPR. Histological examination of the resected specimens revealed tumour free margins in all cases. Post-operative radiographs and CT show resection and reconstruction as planned in all cases. Several learning points were identified related to juvenile bony anatomy and intra-operative registration. Discussion. The use of computer navigation in musculoskeletal oncology allows integration of local anatomy and tumour extent to identify resection margins accurately. Furthermore, it can aid in reconstruction following tumour resection. Our experience thus far has been encouraging

Background. Limb length discrepancy after total hip replacement is one of the possible complications of suboptimal positioning of the implant and cause of patients dissatisfaction. Computer assisted navigation become affirmed in last years for total hip replacement surgery and it is also used for the evaluation of the intra-operative limb length discrepancy. The purpose of this study is to verify the reliability of a navigation system with a dedicated software in intraoperative evaluation of limb lengthening and offset as compared with manual technique. Methods. Forty patients who underwent a Total Hip Arthroplasty in our institution were entrolled in this study. Twenty patients were evaluated with pre operative manual planning (group A) and treated with hand positioning of femoral stem. Twenty Patient were evaluated with preoperative manual planning and treated with Computer assisted navigation of Stem (group B). Mean operating time and blood loss were analyzed. Radiological and clinical follow up was made at 1, 3, 6 and 12 months postoperative to assess any mismatch of implant, complications and clinical results that was measured with Harris Hip Score. Results. In the evaluation of the limb length and offset in group A there wasn't significance difference between pre and postoperative measurements obtained with manual planning. Also in group B there wasn't a significance difference between the measurement obtained intraoperative with computer assisted navigation and the one obtainedafter surgery and preoperative with manual planning. In any case we noted a limb length discrepancy in this series. No statistically significance difference was noted between the two groups in relations to the others parameters investigated. Conclusions. Based on our study the computer navigation system is a simple and reliable for the evaluation of limb length discrepancy and offset in total hip replacement. This Navigation system can offer to the surgeon a valid intraoperative information that can reduce possible errors in stem positioning and can reduce rate of length discrepancy

Objective:. Periacetabular spherical osteotomy for the treatment of dysplastic hip is effective but technically demanding. To help surgeons perform this difficult procedure reliably and safely, a computer assisted navigation technique has been developed and evaluated. Methods:. Computed tomographic scans of 5 cadaveric pelvises were obtained and three-dimensional models were generated. The osteotomy was planned preoperatively. The pelvises were registered using an optimized algorithm. Periacetabular spherical osteotomy was performed at one side of each pelvis with navigation and at another side without navigation. The deviation of the real osteotomized surface from the planned surface was measured. Results:. The computer assisted navigation system supported preoperative planning and provided real time display of the surgical procedure. The deviation of the real osteotomized surface from the planned surface was 1.59 ± 0.18 mm in the group with navigation, while 4.81 ± 1.67 mm in the group without navigation. The difference of the deviations has statistical significance (p < 0.003). Conclusion:. A computer assisted navigation technique is able to help increase accuracy and safety of periacetabular spherical osteotomy, and thus facilitate performing this difficult procedure

Introduction. Total hip arthroplasty has become an increasingly common procedure. Improper cup position contributes to bearing surface wear, pelvic osteolysis, dislocations, and revision surgery. The incidence of cup malposition outside of the safe zone (40° ± 10° abduction and 15° ± 10° anteversion) using traditional techniques has been reported to be as high as 50%. Our hypothesis is that computer assisted navigation will improve cup placement in total hip arthroplasty compared with traditional techniques. Methods. This study retrospectively evaluated the position of 425 consecutive cups placed during primary total hip arthroplasty performed over a two-year period, from 8/1/2012 to 8/1/2014. All cups were placed with a direct-anterior muscle-sparing approach with computer-assisted imageless navigation by a single surgeon. Real-time intraoperative “screen shots” were taken of cup placement. Standard antero-posterior postoperative radiographs of the pelvis were taken within 6 weeks of surgery in the operating surgeon's office using the same standardized protocol for each patient. The radiographs were evaluated by two separate investigators for final abduction and anteversion utilizing the same method as other studies. Statistics were descriptive in nature. Results. Intraoperative navigation screenshots from 425 hips showed that 100% were within the safe zone for abduction and anteversion. Postoperative radiographic review showed that 97% were within the safe zone for abduction (Mean 41 degrees, Range 29–54 degrees), 96% were within the safe zone for anteversion (Mean 16 degrees, Range 4–38 degrees) and 94% were within the safe zone for both abduction and anteversion. Conclusion. In our series, computer assisted navigation improved cup placement in total hip arthroplasty compared with traditional techniques as reported in current literature. Cup position in our study, was within the safe zone for abduction and version at a comparable rate to similar studies examining THA's performed with navigation

Introduction. Recently, tibial insert design of cruciate-substituting (CS) polyethylene insert is employed and widely used. However, in vivo kinematics of using CS polyethylene insert is still unclear. In this study, it is hypothesized that CS polyethylene insert leads to stability of femoro-tibial joint as well as posterior-stabilized (PS) polyethylene insert, even if PCL is sacrificed after TKA. The purpose of this study is an investigation of in vivo kinematics of femoro-tibial joint with use of CS polyethylene insert before and after PCL resction using computer assisted navigation system and tensor device intra-operatively in TKA. Materials and Methods. Sixty-one consecutive patients who had knees of osteoarthritis with varus deformity were investigated in this study. All TKAs (Triathlon, Stryker) were performed using computer assisted navigation system. During surgery, using a tensor device, after bony cut of femur and tibia, joint gaps were assessed in 0 and 90 degrees in flexion. Then, CS polyethylene tibial trial insert were inserted after trial implantation of femoral and tibial components, before and after resection of PCL, respectively. The kinematic parameters of the soft-tissue balance, and amount of coronal and sagittal relative movement between femur and tibia were obtained by interpreting kinematics, which display tables throughout the range of motion (ROM) in the navigation system. In each ROM (30, 45, 60, 90, max degrees), the data were analyzed with a ANOVA test, and mean values were compared by the multiple comparison test (Turkey HSD test) (p< 0.05). Results. Joint gap assessment revealed significant enlargement in both of extension and 90 degrees in flexion after PCL resection compared with before resection. In kinematic analyses in navigation system, regarding to amount of sagittal movement of tibia, there were significances between before and after PCL resection in 60 and 90 degrees in flexion, 1.2mm difference in 60 degrees, and 2.3mm difference in 90 degrees in flexion. There were no significance between before and after PCL resection in the other degrees in flexion. Regarding to the other analyses, varus/ valgus and rotation, there were no differences between before and after resection of PCL. In addition, concerning ROM, maximum extension angle is significantly lower, and maximum flexion angle is significantly higher after than before PCL resection. Discussion. These results demonstrated that CS polyethylene insert might have a stability of femoro-tibial joint nearly after PCL resection as well as before PCL resection. The main design feature of Triathlon CS insert is single radius and rotary arc, in addition, the posterior lip is same as that of Triathlon CR, which can be the factor to avoid paradoxical anterior movement and to permit internal and external rotation between femoral and tibial component. Due to the design features and benefits, there is a high possibility that use of CS insert without PCL can lead same stability as PCL remained, and improvement of ROM. Based on these backgrounds, it is suggested that CS insert may have an additional choice of PCL resection in case of tight gap of flexion in TKA

Introduction. Pedicle screw fixation is considered gold standard as it provides stable and adequate fixation of all the three columns of spine. Mal-placement of screws in dorso-lumbar region, using fluoroscopic control only, varies from 15% to 30 %. The aim of this study was to determine whether accuracy of pedicle screw placement can be improved using CT based navigation technique. Material & methods. 15 patients with fracture of D12 in 4 patients, L1 in 6 patients, L2 in 4 patients, and L4 in 1 patient underwent pedicle screw fixation using CT based navigation. Each fracture was fixed with 4 pedicle screws, 2 each in one level above and one level below the fractured vertebrae. A total of 60 pedicle screws was inserted. A pre-operative 1mm slice planning CT scan was taken from two levels above to two levels below the fractured vertebrae. It was loaded into the workstation and pre-operative planning was made of screw trajectory and screw size i.e. thickness and length, according to the dimensions of the pedicle and vertebral body. Screws were then inserted using opto-electronic navigation system. Screw placement was analysed in all patients using post-operative CT scan and graded according to the Laine's system. Results. The average time for matching was 10.8 minutes and average time for screw insertion was 4.3 minutes (range 2-8 minutes). One screw in right sided pedicle of L2 perforated the lateral cortex (1.66%). There was no neuro-vascular complication. Conclusion. The incidence of a misplaced screw in the present study is only 1.66% which is much less than reported with conventional technique, reflecting enhanced accuracy with computer assisted navigation. Thus computer assisted navigation is a potent tool in the hands of a spine surgeon in improving the accuracy of pedicle screw placement

Introduction. Recently, tibial insert design of cruciate-substituting (CS) polyethylene insert is employed. However, in vivo kinematics of using CS polyethylene insert is still unclear. In this study, it is hypothesized that CS polyethylene insert leads to stability of femolo-tibial joint as well as posterior-stabilized (PS) polyethylene insert, even if PCL is sacrificed after TKA. The purpose of this study is an investigation of in vivo kinematics of femolo-tibial joint with use of CS polyethylene insert before and after PCL resction using computer assisted navigation system intra-operatively in TKA. Materials and Methods. Twenty-four consecutive patients who had knees of osteoarthritis with varus deformity were investigated in this study. All TKAs (Triathlon, Stryker) were performed using computer assisted navigation system. In all patients, difference between extension and flexion gap was under 3mm after bony cut of femur and tibia. During surgery, CS polyethylene tibial trial insert were inserted after trial implantation of femoral and tibial components, before and after resection of PCL, respectively. The kinematic parameters of the soft-tissue balance, and amount of coronal (valgus/varus), sagittal (anterior/posterior) and rotational relative movement between femur and tibia were obtained by interpreting kinematics, which display tables throughout the range of motion (ROM) (Figure1). During record of kinematics, the surgeon gently lifted the experimental thigh three times, flexing the hip and knee. In each ROM (30, 45, 60, 90, max degrees), the data were analyzed with paired t-test, and an ANOVA test, and mean values were compared by the multiple comparison test (Turkey HSD test) (p < 0.05). Results. In coronal (valgus/varus) movement, there are no difference between before and after resection of PCL in all ROM. Regarding to amount of sagittal movement of tibia, tibia was slightly shifted approximately 0.75mm posteriorly in 60 degrees of flexion (p=0.013). There are no significance between before and after PCL resection in the other ROM. In addition, concerning ROM, maximum extension angle is significantly lower, and maximum flexion angle is significantly higher after than before PCL resection. Discussion. These results demonstrated that CS polyethylene insert might have a stability of femoro-tibial joint nearly after PCL resection as well as before PCL resection. The main design feature of Triathlon CS insert is single radius and rotary arc, in addition, the posterior lip is same as that of Triathlon CR, which can be the factor to avoid paradoxical anterior movement and to permit internal and external rotation between femoral and tibial component. This study was localized at point of certain situation that difference between extension and flexion gap is under 3mm after bony cut of femur and tibia during surgery. Due to the design features and benefits, there is a high possibility that use of CS insert without PCL can lead same stability as PCL remained, and improvement of ROM. Based on these backgrounds, it is suggested that CS insert may have an additional choice of PCL resection in case of tight gap of flexion in TKA

Introduction. Recently, tibial insert design of cruciate-substituting (CS) polyethylene insert is employed. However, in vivo kinematics of using CS polyethylene insert is still unclear. In this study, it is hypothesized that CS polyethylene insert leads to stability of femolo-tibial joint as well as posterior-stabilized polyethylene insert, even if posterior cruciate ligament (PCL) is sacrificed after total knee arthroplasty (TKA). The purpose of this study is an investigation of in vivo kinematics of three different tibial insert designs using computer assisted navigation system intra-operatively in TKA. Materials and Methods. Sixty-four consecutive patients who had knees of osteoarthritis with varus deformity were investigated in this study. All TKAs (Triathlon, Stryker, New Jersey, USA) were performed using computer assisted navigation system. During surgery, three different designs of polyethylene tibial trial inserts (PS, CS, and cruciate-retaining (CR) polyethylene insert) were inserted respectively after implantation of femoral and tibial components. The kinematic parameters of the soft-tissue balance were obtained by interpreting kinematics curve, which display bicompartmental gaps throughout the range of motion (ROM) after implantation of each trial insert (Figure. 1). During record of kinematics, the surgeon gently lifted the experimental thigh three times, flexing the hip and knee. Deviation of these three values in each ROM was calculated in each tibial insert in each patient for descriptive analysis. Results. Regarding to values of compartmental gaps, there are no significance between three inserts in both medial and lateral compartments (Figure 2a, b). On medial compartmental gaps, the values of deviations were significantly higher in CR insert than both of PS and CS insert in ROM of over 45 degrees in extension (Fig 3a). In addition, concerning lateral compartmental gaps, the values of deviations were significantly higher in CS insert than both PS and CS insert in all ROM (Fig 3b). Furthermore, there was no significance between PS and CS insert in overall range of motion in both medial and lateral compartmental gaps (Fig 3a, b). Discussion. These results demonstrated that CS polyethylene insert has a stability of femoro-tibial joint nearly as well as PS polyethylene insert. While PS insert may leads to surface damage on open box and has necessity of cutting more bone of femur, some problems involving management of PCL are enumerated in CR inserts. The main design feature of Triathlon CS insert is single radius and rotary arc, in addition, the posterior lip is same as that of Triathlon CR, which can be the factor to avoid paradoxical anterior movement and to permit internal and external rotation between femoral and tibial component. Due to the design features and benefits, there is a high possibility that CS insert can lead same ROM as PS insert, although PS design can produce more ROM than the other type of insert type. Based on these backgrounds, it is suggested that CS insert may have an additional choice in TKA with some advantages especially in concerning of high activity patients like middle aged patients

Introduction. Acquiring adaptive soft-tissue balance is one of the most important factors in total knee arthroplasty (TKA). However, there have been few reports regarding to alteration of tolerability of varus/valgus stress between before and after TKA. In particular, there is no enough data about mid-flexion stability. Based on these backgrounds, it is hypothesized that alteration of varus/valgus tolerance may influence post-operative results in TKA. The purpose of this study is an investigation of in vivo kinematic analyses of tolerability of varus/valgus stress before and after TKA, comparing to clinical results. Materials and Methods. A hundred knees of 88 consecutive patients who had knees of osteoarthritis with varus deformity were investigated in this study. All TKAs (Triathlon, Stryker) were performed using computer assisted navigation system. The kinematic parameters of the soft-tissue balance, and amount of coronal relative movement between femur and tibia were obtained by interpreting kinematics, which display graphs throughout the range of motion (ROM) in the navigation system. Femoro-tibial alignments were recorded under the stress of varus and valgus before the procedure and after implantation of all components. In each ROM (0, 30, 60, 90, 120 degrees), the data of coronal relative movement between femur and tibia (tolerability) were analyzed before and after implantation. Furthermore, correlations between tolerability of varus/valgus and clinical improvement revealed by ROM and Knee society score (KSS) were analyzed by logistic regression analysis. Results. Evaluation of soft tissue balance with navigation system revealed that the tolerance of coronal relative movement between femur and tibia (varus/valgus) after implantation was significantly decreased compared with before implantation even in mid-flexion range. There were no significant correlations between tolerability of coronal relative movement and improvement of extension range and KSS. However, mid-flexion tolerability showed negative correlation with flexion range. Discussion. One of the most important principles for ligament balancing in TKA for varus knees is involved that the medial extension gap should be within 1–3mm to avoid flexion contracture and a feeling of instability, the medial flexion gap should be equal or 1–2mm larger to the medial extension gap, and lateral extension laxity up to 5 degrees is acceptable. However, there have been few reports measuring laxity from 30 to 60 degrees. In this study, the tolerance of coronal relative movement was significantly limited even in mid-flexion. However, mid-flexion tightness was not significantly correlated with clinical results except for flexion range. This result might be suggested that high tolerability of coronal relative movement in mid-flexion range may lead to widening of flexion range of motion of the knee after TKA. For any figures or tables, please contact authors directly

Alignment and soft tissue balance are two of the most important factors that influence early and long term outcome of total knee arthroplasty. Current clinical practice involves the use of plain radiographs for preoperative planning and conventional instrumentation for intra operative alignment. The aim of this study is to assess the Signature. TM. Personalised system using patient specific guides developed from MRI. The Signature. TM. system is used with the Vanguard. R. Complete Knee System. This system is compared with conventional instrumentation and computer assisted navigation with the Vanguard system. Patients were randomised into 3 groups of 50 to either Conventional Instumented Knee, Computer Navigation Assisted Knee Arthroplasty or Signature Personalised Knee Arthoplasty. All patients had the Vanguard Total knee Arthroplasty Implanted. All patients underwent Long leg X-rays and CT Scans to measure Alignment at pre-op and 6 months post-op. All patients had clinical review and the Knee Society Score (KSS) at 1 year post surgery was used to measure the outcome. A complete dataset was obtained for 124 patients. There were significant differences in alignment on Long leg films ot of CT scan with perth protocol. Notably the Signature group had the smallest spread of outliers. In conclusion the Signature knee system compares well in comparison with traditional instrumentation and CAS Total Knee Arthroplasty

Objective. To compare between the CAMISS-TLIF group and the OP-TLIF group in the clinical efficacy and radiographic manifest. Methods. This study was a registration study, selected 27 patients with lumbar spondylolisthesis from May 2011 to March 2014 in our hospital. Patients in one group are treated with computer assisted navigation minimally invasive TLIF (CAMISS -TLIF) while the others are treated with the OP-TLIF (OPEN-TLIF). The former group has 13 cases while the latter group has 14 cases. We collected information and present statistical analysis on the following aspects in order to compare the two different surgical methods of treatment. They are the operation duration, blood loss, days of hospitalisation, the preoperative and follow-up JOA and JOA improvement rate, the preoperative and follow-up ODI scores, the preoperative and follow-up VAS and Odom's criteria. By analysing the follow-up CT results, we compare the pedicle screw accuracy rate between the two groups in order to make a comprehensive assessment of these two surgical methods. Results. There is a significant difference in blood loss, follow-up JOA improvement rate and follow-up ODI scores between the CAMISS-TLIF group and OP-TLIF group (P <0.05), while in other fields there is no statistically significant differences. Conclusion. CAMISS-TLIF surgical approach has an advantage of less blood loss, less muscle stripping, smaller surgical trauma and more quickly recovery after surgery

Background. When positioning and rotating the femoral cutting block (AP) on the femur it can either be done according to bony landmarks (measured resection) or by tensioning the flexion gap and positioning it parallel to the tibia (gap balanced technique.) Accurate rotation of the femoral component is essential to ensure a symmetric flexion gap to ensure optimal tibio-femoral kinematics and patello-femoral tracking. Methods. 74 consecutive total knee replacements were assessed intra-operatively for symmetry of the flexion gap by applying a varus and a valgus stress and digitally recording the opening with a computer assisted navigation system. External rotation of the femoral component according to the bony landmarks was measured radiologically. This was compared to the external rotation suggested by the navigation intra-operatively using a gap balanced workflow. Results. The gap balanced technique gave a symmetric flexion gap with less than 3 mm side to side difference in 95% of cases. In 84% of cases (62 of 74) the gap balanced technique was more accurate than the measured resection technique in determining femoral rotation. In 16 % of cases (12 of 74) the same rotation was measured with the two techniques. In no case was the measurement more accurate with the measured resection technique. This result was highly statistically significant. Conclusion. The gap balanced technique is more accurate than measured resection for determining axial rotation of the femoral component in total knee arthroplasty. NO DISCLOSURES

Background. Coronal malalignment has been proposed as a risk factor for mechanical failure after total knee arthroplasty (TKA). In response to these concerns, technologies that provide intraoperative feedback to the surgeon about component positioning have been developed with the goal of reducing rates of coronal plane malalignment and improving TKA longevity. Imageless hand-held portable accelerometer technology has been developed to address some the limitations associated with other computer assisted navigation devices including line-of-sight problems, preoperative imaging requirements, extra pin sites, up-font capital expenditures, and learning curve. The purpose of this study was to compare the accuracy and precision of a hand-held portable navigation system versus conventional instrumentation for tibial and femoral resections in TKA. Methods. This study was a single-surgeon, retrospective cohort study. Consecutive patients undergoing TKA were divided into three groups: 1) tibial and femoral resections performed with conventional intra- and extramedullary resection guides (CON group; N=84), 2) a hand-held portable navigation system (KneeAlign, OrthoAlign Inc, Aliso Viejo, CA) for tibial resection only (TIBIA group; N=78), and 3) navigation for both tibial and distal femoral resections (BOTH group; N=80). Postoperative coronal alignment of the distal femoral and proximal tibial resection were measured based on the anatomic axis from standing AP radiographs and compared between the three groups for both precision and accuracy. Malalignment was considered to be greater than 3° varus/valgus from expected resection angle. Results. Preoperative age, sex, and knee axis alignment were similar between the three groups. Mean postoperative alignment of the distal femoral resection, proximal tibial resection, and knee axis did not differ between groups (Figure 1). Increased frequencies of malalignment (±3° varus/valgus) of the femoral resection (24% CON versus 5% TIBIA and 8% BOTH; p<0.001) and knee axis (31% CON versus 8% TIBIA and 6% BOTH; p<0.001) were observed with conventional resection guides compared to both navigation groups. Conclusion. Use of a hand-held portable navigation system improved precision of the distal femoral resection and overall anatomical knee alignment after TKA

The surgical management of musculoskeletal tumours is a challenging problem, particularly in pelvic and diaphyseal tumour resection where accurate determination of bony transection points is extremely important to optimise oncologic, functional and reconstructive options. The use of computer assisted navigation in these cases could improve surgical precision. We resected musculoskeletal tumours in fifteen patients using commercially available computer navigation software (Orthomap 3D). Of the eight pelvic tumours, three underwent biological reconstruction with extra corporeal irradiation; three endoprosthetic replacement (EPR) and two required no bony reconstruction. Four diaphyseal tumours had biological reconstruction. Two patients with proximal femoral sarcoma underwent extra-articular resection and EPR. One soft tissue sarcoma of the adductor compartment involving the femur was resected with EPR. Histological examination of the resected specimens revealed tumour free margins in all cases. Post-operative radiographs and CT show resection and reconstruction as planned in all cases. Several learning points were identified related to juvenile bony anatomy and intra-operative registration. The use of computer navigation in musculoskeletal oncology allows integration of local anatomy and tumour extent to identify resection margins accurately. Furthermore, it can aid in reconstruction following tumour resection. Our experience thus far has been encouraging

INTRODUCTION. Total knee replacement is mostly done with alignment rods in order to achieve a proper Varus / Valgus alignement. Other techniques are computer assisted navigation or MRI based preoperative planning. iASSIST™ is a computer assisted stereotaxic surgical instrument system to assist the surgeon in the positioning of the orthopaedic implant system components intra-operatively. It is imageless and the communication between the PC and the “Pod's” does not require any direct camera view, it is a bluethooth comunication system. This study presents preliminary results utilizing iASSIST™. The aim of this study was to test and compare radiographic alignment, functional outcomes, and perioperative morbidity of the iASSIST™ Knee system versus conventional total knee arthroplasty. METHODS. In a prospective randomized trial we investigated 60 patients with osteoarthritis of the knee joint. Each surgical procedure was conducted by highly experienced surgeons. In both groups the implant Legacy LPS-Flex Fixed Bearing Knee was used (Zimmer®, Warsaw, Indiana). The groups were equally divided and randomized by hazard. For clinical evaluation, the Short Form-36 and Knee Society Score were obtained. For the radiological assessment mediCAD® Classic, a digital measurement system, was used. The aim of the study was the comparison of results after 3 months. Results. 2 patients refused any further participation, and 5 cases required a switch to a conventional alignement technique intraoperatively due to technical problems. Average BMI and average age did not differ in both groups. Surgical time in the iASSIST™ group amounted to 100 minutes, in the conventional group to 76 min. Postoperative functional outcomes were statistically insignificant, showing slight improvements of the Combined Knee Society Score, Knee Society Knee Score, and Knee Society Function Score favouring the iASSIST method, and slight improvements of knee flexion. Short Form-36 physical scales slightly favoured the conventional method but not significantly. The mean deviation from neutral mechanical axis was 1.68°±1.9° within the iASSIST group, and 2.73°±2.1° within the conventional TKA group. Conclusion. IASSIST™ is a valuable computer navigation system. The 5 technical troubles were due to the learning curve. The clinical results after 3 months did not differ significantly, the radiological assessment showed a tendency of improved alignement in the iASSIST™ group

Lower limb alignment after unicondylar knee arthroplasty (UKA) has a significant impact on surgical outcomes. The literature lacks studies that evaluate the limb alignment after lateral UKA or compare it to alignment outcomes after medial UKA, making our understanding of this issue based on medial UKA studies. Unfortunately, since the geometry, mechanics, and ligamentous physiology are different between these two compartments, drawing conclusions for lateral UKAs based on medial UKA results may be imprecise and misleading. The purpose of this study was to compare the risk for limb alignment overcorrection and the ability to predict postoperative limb alignment between medial and lateral UKA. We evaluated the results of mechanical limb alignment in 241 patients with unicompartmental knee osteoarthritis who underwent medial or lateral UKA; there were 229 medial UKAs and 37 lateral UKAs. Mechanical limb alignment was measured in standing long limb radiographs pre and post-operatively, intra-operatively it was measured using a computer assisted navigation system. Between the two cohorts, we compared the percentage of overcorrection and the difference between post-operative alignment and alignment measured by the navigation system. The percentage of overcorrection was significantly higher in the lateral UKA group (11%), when compared to the medial UKA group (4%), (p= 0.0001). In the medial UKA group, the mean difference between the intraoperative “virtual” alignment provided by the navigation system, and the post-operative, radiographically measured mechanical axis, was 1.33°(±1.2°). This was significantly lower than the mean 1.86° (±1.33°) difference in the lateral UKA group (p=0.019). Our data demonstrated an increased risk of mechanical limb alignment overcorrection and greater difficulty in predicting postoperative alignment using computer navigation, when performing lateral UKAs compared to medial UKAs

Lower limb alignment after unicondylar knee arthroplasty (UKA) has a significant impact on surgical outcomes. The literature lacks studies that evaluate the limb alignment after lateral UKA or compare it to alignment outcomes after medial UKA, making our understanding of this issue based on medial UKA studies. Unfortunately, since the geometry, mechanics, and ligamentous physiology are different between these two compartments, drawing conclusions for lateral UKAs based on medial UKA results may be imprecise and misleading. The purpose of this study was to compare the risk for limb alignment overcorrection and the ability to predict postoperative limb alignment between medial and lateral UKA. We evaluated the results of mechanical limb alignment in 241 patients with unicompartmental knee osteoarthritis who underwent medial or lateral UKA; there were 229 medial UKAs and 37 lateral UKAs. Mechanical limb alignment was measured in standing long limb radiographs pre and post-operatively, intra-operatively it was measured using a computer assisted navigation system. Between the two cohorts, we compared the percentage of overcorrection and the difference between post-operative alignment and alignment measured by the navigation system. The percentage of overcorrection was significantly higher in the lateral UKA group (11%), when compared to the medial UKA group (4%), (p= 0.0001). In the medial UKA group, the mean difference between the intraoperative “virtual” alignment provided by the navigation system, and the post-operative, radiographically measured mechanical axis, was 1.33°(±1.2°). This was significantly lower than the mean 1.86° (±1.33°) difference in the lateral UKA group (p=0.019). Our data demonstrated an increased risk of mechanical limb alignment overcorrection and greater difficulty in predicting postoperative alignment using computer navigation, when performing lateral UKAs compared to medial UKAs

Computer assisted surgical navigation has played an increasingly central role in total knee arthroplasty (TKA). Given the recognized importance of subtle component position changes in knee function, navigation has emerged as a promising tool for reducing the occurrence of significant malalignment. The ability of this technology to reliably measure multiple parameters intraoperatively allows analysis to possibly identify a correlation between intraoperative computer assisted surgical navigation data and functional outcomes of patients undergoing elective total knee arthroplasty. Intraoperative navigation data was collected for 121 patients undergoing cemented, posterior stabilized TKA. Three forward stepwise regression analyses were performed to associate intraoperative coronal alignment correction, tibiofemoral external rotation, and alignment under varus and valgus stress with one year outcomes, including range of motion, Oxford and SF-36 scores. The amount of alignment correction and the maximum flexion achieved intraoperatively were significantly correlated (p <0.05, R-sq = 13%) with clinically measured maximum flexion at one year. Maximum flexion achieved intraoperatively, external tibiofemoral rotation and maximum varus under stress were also significantly associated (p < 0.05, R-sq = 31%) with the physical component of the SF-36 outcome score. Analyses of computer navigation in TKA to date have primarily focused on precision of sagittal plane correction. Alternatively we have identified four intraoperative parameters that correlate with functional outcome at one year. Correct intraoperative interpretation of navigation data may allow surgeons to make subtle changes in real time to produce superior short-term outcomes for patients

Restoring the overall mechanical alignment to neutral has been the gold standard since the 1970s and remains the current standard of knee arthroplasty today. Recently, there has been renewed interest in alternative alignment goals that place implants in a more “physiologic” position with the hope of improving clinical outcomes. Anywhere from 10 – 20% of patients are dissatisfied after knee replacement surgery and while the cause is multifactorial, some believe that it is related to changing native alignment and an oblique joint line (the concept of constitutional varus) to a single target of mechanical neutral alignment. In addition, recent studies have challenged the long held belief that total knee placed outside the classic “safe zone” of +/− 3 degrees increases the risk of mechanical failure which theoretically supports investigating alternative, more patient specific, alignment targets. From a biomechanical, implant retrieval, and clinical outcomes perspective, mechanical alignment should remain the gold standard for TKA. Varus tibias regardless of overall alignment pattern show increased polyethylene wear and varus loading increases the risk of posteromedial collapse. While recently questioned, the evidence states that alignment does matter. When you combine contemporary knee designs placed in varus with an overweight population (which is the majority of TKA patients) the failure rate increases exponentially when compared to neutral alignment. A recent meta-analysis on mechanical alignment and survivorship clearly demonstrated reduced survivorship for varus-aligned total knees. The only way to justify the biomechanical risks associated with placing components in an alternative alignment target is a significant clinical outcome benefit but the evidence is lacking. A randomised control trial comparing mechanical alignment (MA) and kinematic alignment (KA) found a significant improvement in clinical outcomes and knee function in KA patients at 2 year follow-up. In contrast, Young et al. recently published a randomised control trial comparing PSI KA and computer assisted mechanical TKA and found no difference in any clinical outcome measure. Why were the clinical outcomes scores in the MA patients so different: One potential explanation is that different surgical techniques were used. In the Dosset study, the femur was cut at 5 degrees valgus in all patients and femoral component rotation was always set at 3 degrees externally rotated to the posterior condylar axis. We know from several studies that this method leads to inaccuracies in both coronal plane and axial plane in some patients. Young et al. used computer assisted navigation to align his distal femur cut with the mechanical axis and adjusted femoral component rotation to the transepicondylar axis. The results suggest that a well performed mechanical aligned total knee replacement has excellent clinical performance equal to that of kinematic alignment without any of the long term risks of implant failure. Most contemporary TKA implants are designed to be loaded perpendicular to the polyethylene surface and placing them in shear without extensive biomechanical testing to support this alignment target may put patients at long term risk for an unproven benefit. Have we not learned our lesson?

Hypothesis. Custom cutting blocks can produce similar alignment compared to computer navigated and conventional total knee arthroplasty (TKA) techniques. Method. We conducted a retrospective review of 37 patients who underwent TKA by a single surgeon in a teaching hospital setting. Groups were conventional method (10), computer assisted navigation (10), and custom blocks (18). The custom group was further subdivided to CT and MRI based blocks. Post-operative alignment was measured (blinded) using full length weight bearing radiographs at 18 weeks on average. Hospital records were reviewed to determine operative time, transfusion requirements, length of hospital stay, complications and cost. Results. Post-operative mechanical axis was within 3 degrees of neutral in 100% of the navigation group, 70% of the conventional group and 50% of the custom block group. Average alignment was within 1.8, 3.1 and 3.6 degrees of neutral for each group respectively. The operative time was greater for the computer navigation group (86.7 min) compared to the conventional (72.1) and MRI custom block groups which involved unfamiliar instrumentation (73.8). CT based block procedures involved otherwise familiar instruments and averaged 61.2 minutes. Length of hospital stay and complications were similar for all three groups. Total cost was the least for the conventional group. Increased costs were associated with computer equipment, pre-operative advanced imaging and custom blocks. Conclusions. Custom cutting blocks in this small series obtain worse radiographic positioning of total knee arthroplasty components compared to conventional and computer navigation techniques. Further studies with greater number of patients, CT alignment analysis and long-term follow-up are required