As previous meta-analyses on the alignment outcomes of Computer-assisted orthopaedic surgery (CAOS) did not differentiate between CAOS systems, limited information is available on the accuracy of a specific CAOS system based on clinical cases. This study assessed the accuracy and precision of achieving surgical goals in approximately 7000 cases using a specific contemporary CAOS system. Alignment parameters were extracted from the technical logs of 6888 TKA surgeries performed between October 2012 and January 2017 using a contemporary CAOS system. The following surgical parameters were investigated: 1) planned resection defined by the surgeon prior to the bone cuts; 2) Checked resection defined as digitalisation of the bony cuts. Deviations in alignment between planned and checked resections were evaluated, with acceptable resections defined as no more than 3° of resection deviations. For the tibial resection, deviations in tibial varus/valgus angle and posterior tibial slope were 0.06 ± 0.94° and −0.09 ± 1.73°, respectively. For the femoral resection, deviations in femoral varus/valgus angle amd femoral flexion were 0.00 ± 0.97° and −0.17 ± 1.44°, respectively. High percentages of the resections were found to be acceptable (>94% of the cases). The CAOS system investigated was shown to provide accurate and precise intra-operative assistance to the surgeon in achieving targeted resections. The study summarised a large number of cases spanning the application history of the specific CAOS system, including both experienced users and new adopters of the technology. The data provided a complete clinical relevant evaluation demonstrating its high accuracy and precision in resection alignment.
Computer-assisted orthopaedic surgery (CAOS) has been demonstrated to increase accuracy to component alignment of total knee arthroplasty compared to conventional techniques. The purpose of this study was to assess if learning affects resection alignment using a specific CAOS system. Nine surgeons, each with >80 TKA experience using a contemporary CAOS system were selected. Prior to the study, six surgeons had already experienced with CAOS TKA (experienced), while the rest three were new to the technology (novice). The following surgical parameters were investigated: 1) planned resection, resection parameters defined by the surgeon prior to the bone cuts; 2) checked resection, digitalisation of the realised resection surfaces. Deviations in the alignment between planned and checked resections were compared between the first 20 cases (in learning curve) and the last 20 cases (well past learning curve) within each surgeon. Any significance detected (p < 0.05) with >1° difference in means indicated clinically meaningful impact on alignment by the learning phase. Both pooled and surgeon-specific analysis exhibited no clinically meaningful significant difference between the first 20 and the last 20 cases from both experienced and novice surgeon groups. The resections in both the first 20 and the last 20 cases demonstrated acceptable rates of over 95% in alignment (<3° deviation) for both experienced and novice surgeons. This study demonstrated that independent of the surgeon's prior CAOS experiences, the CAOS system investigated can provide an accurate and precise solution to assist in achieving surgical resection goals with no clinically meaningful compromise in alignment accuracy and outliers during the learning phase.
Despite that computer-assisted orthopaedic surgery (CAOS) has been shown to offer increased accuracy to the bony resections compared to the conventional techniques [1], previous studies of CAOS have mostly focused on alignment outcomes based on a small number of patients [1]. Although several recent meta-analyses on the CAOS outcomes have been reported [2], these analyses did not differentiate between systems, while system-dependency has been reported to influence alignment parameters [3]. To date, no study has benchmarked a specific CAOS system based on a large number of clinical cases. The purpose of this study is to assess the accuracy and precision of bony resection in more than 4000 cases using a specific contemporary CAOS system. Technical logs of 4292 TKAs performed between October 2012 and January 2016 using a contemporary CAOS system (ExactechGPS, Blue-Ortho, Grenoble, FR) were analyzed. The analyses were performed on: 1) planned resection, defined by the surgeon prior to the bone cuts. These parameters serve as inputs for the CAOS guidance; and 2) Checked resection, defined as digitalization of the actual resection surfaces by manually pressing an instrumented checker onto the bony cuts. Deviations in alignment and resection depths (on the referenced side) between planned and checked resections were calculated in coronal and sagittal planes for both tibia and femur (planned vs checked).INTRODUCTION
Materials and Methods
Although several meta-analyses have been performed on total knee arthroplasty (TKA) using computer-assisted orthopaedic surgery (CAOS) [1], understanding the inter-site variations of the surgical profiles may improve the interpretation of the results. Moreover, information on the global variations of how TKA is performed may benefit the development of CAOS systems that can better address geographic-specific operative needs. With increased application of CAOS [2], surgeon preferences collected globally offers unprecedented opportunity to advance geographic-specific knowledge in TKA. The purpose of this study was to investigate geographic variations in the application of a contemporary CAOS system in TKA. Technical records on more than 4000 CAOS TKAs (ExactechGPS, Blue-Ortho, Grenoble, FR) between October 2012 and January 2016 were retrospectively reviewed. A total of 682 personalized surgical profiles, set up based on surgeon's preferences, were reviewed. These profiles encompass an extensive set of surgical parameters including the number of steps to be navigated, the sequence of the surgical steps, the definition of the anatomical references, and the parameters associated with the targeted cuts. The profiles were compared between four geographic regions: United States (US), Europe (EU), Asia (AS), and Australia (AU) for cruciate-retaining (CR) and posterior-stabilized (PS) designs. Clinically relevant statistical differences (CRSD, defined as significant differences in means ≥1°/mm) were identified (significance defined as p<0.05).INTRODUCTION
Materials and Methods
While multiple factors contribute to the variability of prosthesis placement during total knee arthroplasty (TKA), the accuracy of the surgeon's resection planning (positioning of the cutting block) is arguably the most critical. One may postulate that proper training, including enabling the surgeon to passively receive quantitative feedback on the cutting block position, may help him/her improve resection accuracy. The purpose of this study was to test the hypothesis that passive reception of feedback on cutting block position improves the accuracy of the successive TKA resection planning. Five cadaveric knees (tibia and foot only) were studied. After arthrotomy, the tracker of an imageless navigation system (ExactechGPS®, Blue-Ortho, Grenoble, FR) was attached to the tibia. A navigated TKA procedure was initiated starting with registration of anatomical landmarks. Four surgeons then positioned the tibial cutting block (without pinning) on each knee using standard extramedullary mechanical instruments. The planned target resection was neutral varus/valgus, 3° posterior slope, and 10mm resection depth referencing the lateral plateau. Each surgeon performed 3 planning trials on each of the 5 knees, removing the cutting block between attempts. The planned resections were measured using an instrumented checker provided with the navigation system, referencing the cutting block. Surgeons were informed of the resection parameters measured by the navigation system after each planning trial. The deviations in resection parameters between the resection target and the cutting block position were calculated for each planning trial. The effect of receiving passive feedback on the accuracy of successive placement of the cutting block was assessed by comparing the deviations between each surgeon's 3 trials on the same cadaver (paired-t test). Statistical significance was defined as p<0.05.INTRODUCTION
Materials and Methods
Studies have reported that only 70–80% of the total knee arthroplasty (TKA) cases using conventional instruments can achieve satisfactory alignment (within ±3° of the mechanical axis). Computer-assisted orthopaedic surgery (CAOS) has been shown to offer increased accuracy and precision to the bony resections compared to conventional techniques [1]. As the early adopters champion the technology, reservation may exist among new CAOS users regarding the ability of achieving the same results. The purpose of this study was to investigate if there are immediate benefits in the accuracy and precision of achieving surgical goals for the novice surgeons, as compared to the experienced surgeons, by using a contemporary CAOS system. Two groups of surgeons were randomly selected from TKAs between October 2012 and January 2016 using a CAOS system (ExactechGPS, Blue-Ortho, Grenoble, FR), including:
All the surgeries from the INTRODUCTION
Materials and Methods
The alignment of components in total knee arthroplasty (TKA) is perceived to be one of the most influential factors in determining the long-term outcomes. A contemporary debate exists regarding the choice of the alignment method. As a vast majority of the surgeons support the basis of the mechanical alignment philosophy (MA), others believe in the concept of anatomical alignment theory (AA) to closely match the anatomy of the femur and the tibia of the native knee [1]. This study was intended to evaluate the accuracy of achieving a planned tibial resection target using either the MA or AA methods. Five healthy cadaveric knees (tibia and foot only) were studied. Four surgeons were independently asked to position a tibial cutting block (without pinning) using conventional extramedullary mechanical instrumentation (Exactech LPI instrumentation, Gainesville, FL, USA). Surgeons were asked to target a predefined proximal tibial cut according to MA (Varus= 0°, posterior slope= 3°, resection level= 10 mm) or to AA (Varus= 3°, posterior slope= 6°, resection level= 9 mm). Once the surgeon expressed satisfaction with the achieved position of the tibial cutting block, the planned resection was recorded using an imageless guidance system (ExactechGPS®, Blue-Ortho, Grenoble, FR). Surgeons completed at least three positioning trial for each alignment method on each cadaver. The accuracy and outliers (deviated more than 2°/mm from the target [2]) of resection planning were compared between the MA and AA methods. Statistical significance was defined as p< 0.05.INTRODUCTION
Materials and Methods
One main perceived drawback for the adoption of computer assisted orthopedic surgery (CAOS) during total knee arthroplasty (TKA) relates to the increased surgical time compared to the use of standard mechanical instrumentation [1]. This study compared the time efficiency between a next generation CAOS system (ExactechGPS®, Blue-Ortho, Grenoble, FR) and conventional mechanical instrumentation, and assessed the impact of surgeon experience level on the efficiency. Surgical time was retrospectively reviewed on 63 primary TKAs performed by a board-certified orthopedic surgeon (PP) using a cemented postero-stabilized knee system (Optetrak Logic PS, Exactech, Gainesville, FL), grouped as 1) Group I (control): 21 TKAs using conventional mechanical instruments; 2) Group II: 21 TKAs performed using the CAOS system with an early experience level (first 21 cases); and 3) Group III: 21 TKAs using the CAOS system with an advanced experience level (beyond 30 cases). Surgical time was compared across the three groups (with significance defined as p<0.05).Introduction
Materials and methods
Total knee arthroplasty (TKA) can effectively treat end-stage knee osteoarthritis. For cruciate-retaining (CR) TKA, the posterior tibial slope (PTS) of the reconstructed proximal tibia plays a significant role in restoring normal knee kinematics as it directly affects the tension of the posterior cruciate ligament (PCL) [1]. However, conventional cadaveric testing of the impact of PTS on knee kinematics may damage/stretch the PCL, therefore impact the test reproducibility. The purpose of this study was to assess the reproducibility of a novel method for the evaluation of the effects of PTS on knee kinematics. Cemented CR TKAs (Logic CR, Exactech, Gainesville, FL, USA) were performed using a computer-assisted surgical guidance system (ExactechGPS®, Blue-Ortho, Grenoble, FR) on six fresh frozen non-arthritic knees (PCL presumably intact). The tibial baseplate was specially designed (Fig. 1) with a mechanism to modify the PTS in-situ. Knee kinematics, including anteroposterior (AP) translation, internal/external (IE) rotation, and hip-knee-ankle angles, were evaluated by performing a passive range of motion from extension up to ∼110° of flexion, three separate times at 5 PTSs: 10°, 7°, 4°, 1°, and then 10° again. The repeatability of the test was investigated by comparing the kinematics between the first and the last 10° tests. Any clinically relevant deviation (1.5° for the hip knee ankle angle, 1.5mm for anterior-posterior translation and 3° for internal-external rotation) would reflect damage to the soft-tissue envelope or the PCL during the evaluation. Potential damage of PCL was investigated by comparing the kinematic parameters from the first and last 10° slope tests at selected flexion angles (Table 1) by paired t-test, with statistical significance defined as p<0.05.Introduction
Materials and Methods
Evaluations of Computer-assisted orthopaedic surgery (CAOS) systems generally overlooked the intrinsic accuracy of the systems themselves, and have been largely focused on the final implant position and alignment in the reconstructed knee [1]. Although accuracy at the system-level has been assessed [2], the study method was system-specific, required a custom test bench, and the results were clinically irrelevant. As such, clinical interpolation/comparison of the results across CAOS systems or multiple studies is challenging. This study quantified and compared the system-level accuracy in the intraoperative measurements of resection alignment between two CAOS systems. Computer-assisted TKAs were performed on 10 neutral leg assemblies (MITA knee insert and trainer leg, Medial Models, Bristol, UK) using System I (5 legs, ExactechGPS®, Blue-Ortho, Grenoble, FR) and System II (5 legs, globally established manufacturer). The surgeries referenced a set of pre-defined anatomical landmarks on the inserts (small dimples). Post bone cut, the alignment parameters were collected by the CAOS systems (Introduction
Materials and Methods
Computer-assisted orthopaedic surgery (CAOS) has been shown to assist in achieving accurate and reproducible prosthesis position and alignment during total knee arthroplasty (TKA) [1]. The most prevalent modality of navigator tracking is optical tacking, which relies on clear line-of-sight (visibility) between the localizer and the instrumented trackers attached to the patient. During surgery, the trackers may not always be optimally positioned and orientated, sometimes forcing the surgeon to move the patient's leg or adjust the camera in order to maintain tracker visibility. Limited information is known about tracker visibility under clinical settings. This study quantified the rotational limits of the trackers in a contemporary CAOS system for maintaining visibility across the surgical field. A CAOS system (ExactechGPS®, Blue-Ortho, Grenoble, FR) was set up in an operating room by a standard surgical table according to the manufacture's recommendation. A grid with 10×10 cm sized cells was placed at the quadrant of the surgical table associated with the TKA surgical field [Fig. 1A,B]. The localizer was set up to aim at the center of the grid. A TKA surgical procedure was then initiated using the CAOS system. Once the trackers-localizer connection was established, the CAOS system constantly monitored the root mean square error (RMS) of each tracker. The connection was immediately aborted if the measured RMS was above the defined threshold. Therefore, “visibility” was defined as the tracker-localizer connection with proper accuracy level. An F tracker from the tracker set (3 trackers with similar characteristics) was placed at the center of each cell by a custom fixture, facing along the +Y axis [Fig. 1]. The minimum and maximum angles of rotation around the Z axis (RAZ_MIN and RAZ_MAX) and X axis (RAX_MIN and RAX_MAX) for maintaining tracker visibility were identified. For each cell, the rotational limit of the tracker was calculated for each axis of rotation as the difference between the maximum and minimum angles (RLX and RLZ).Introduction
Materials and Methods
While total knee arthroplasty (TKA) improves postoperative function and relieves pain in the majority of patients with end stage osteoarthritis, its ability to restore normal knee kinematics is debated. Cadaveric studies using computer-assisted orthopaedic surgery (CAOS) system [1] are one of the most commonly used methods in the assessment of post-TKA knee kinematics. Commonly, these studies are performed with an open arthrotomy; which may impact the knee kinematics. The purpose of this cadaveric study was to compare the knee kinematics before and after (open or closed) arthrotomy. Kinematics of seven non-arthritic, fresh-frozen cadaveric knees (PCL presumably intact) was evaluated using a custom software application in an image-free CAOS system (ExactechGPS, Blue-Ortho, Grenoble, FR). Prior to the surgical incision, one tracker was attached to the diaphysis of each tibia and femur. Native intact knee kinematics was then assessed by performing passive range of motion (ROM) three separate times, from full extension to at least 110 degrees of flexion, with the CAOS system measuring and recording anatomical values, including flexion angle, internal-external (IE) rotation and anterior-posterior (AP) translation of the tibia relatively to the femur, and the hip-knee-ankle (HKA) angle. Next, an anterior incision with a medial parapatellar arthrotomy was performed, followed by acquisition of the anatomical landmarks used for establishing an anatomical coordinate system in which all the anatomical values were evaluated [2]. The passive ROM test was then repeated with closed and then open arthrotomy (patella manually maintained in the trochlea groove). The anatomical values before and after knee arthrotomy were compared over the range of knee flexion using the native knee values as the baseline.Introduction
Materials and Methods
Computer-assisted orthopaedic surgery (CAOS) has been shown to help achieve accurate, reliable and reproducible prosthesis position and alignment during total knee arthroplasty (TKA) [1]. A typical procedure involves inputting target resection parameters at the beginning of the surgery and measuring the achieved resection after bone cuts. Across CAOS systems, software/hardware design, mechanical instrumentation, and system-dependent work flow may vary, potentially affecting the intraoperative measurement of the achieved resection. This study assessed the cumulative effect of system-dependent differences between two CAOS systems by comparing the alignment deviation between the measurement of the achieved resection and the targeted parameters. TKA resections were performed on 10 neutral whole leg assemblies (MITA knee insert and trainer leg, Medial Models, Bristol, UK) by a board-certified orthopaedic surgeon (BH) using System I (5 legs, ExactechGPS®, Blue-Ortho, Grenoble, FR) and System II (5 legs, globally established manufacturer). The surgeon was deemed as “experienced” user (>30 surgeries) with both systems. The target parameters for the TKA resections, as well as major differences between the two systems are summarized in Table 1A. The deviations of the intraoperative alignment measurements on the achieved distal femoral and proximal tibial resection from the target were calculated and compared between the two systems with significance defined as p<0.05.Introduction
Materials and Methods
Computer-assisted orthopaedic surgery (CAOS) provides great value in ensuring accurate, reliable and reproducible total knee arthroplasty (TKA) outcomes [1,2]. Depending on surgeon preferences or patient factors (e.g. BMI, ligament condition, and individual joint anatomy), resection planning (guided adjustment of cutting blocks) is performed with different knee flexion, abduction/adduction (ABD/ADD) and internal/external (I/E) rotation angles, potentially leading to measurement errors in the planned resections due to a modified tracker/localizer spatial relationship. This study assessed the variation in the intraoperative measurement of the planned resection due to leg manipulation during TKA, and identified the leg position variables (flexion, ABD/ADD, and I/E rotation) contributing to the variability. Computer-assisted TKA (ExactechGPS®, Blue-Ortho, Grenoble, FR) was performed on a neutral whole leg assembly (MITA knee insert and trainer leg, Medial Models, Bristol, UK) by a board-certified orthopaedic surgeon (BH) at his preferred leg flexion, ABD/ADD, and I/E rotation angles. A cutting block was adjusted and fixed to the tibia, targeting the resection parameters listed in Table 1A. An instrumented resection checker was then attached to the cutting block to measure the planned resection at the same leg position (baseline). Next, the surgeon moved the leg to 9 sampled positions, representing typical leg position/orientation associated with different steps during TKA [Table 1B]. The planned resection was tracked by the CAOS system at each leg position. Tibial resection parameters at each sampled position were compared to the baseline. Regression was performed to identify the variables (flexion, ABD/ADD, I/E rotation) that significantly contribute to the measured variation (p<0.05).Introduction
Materials and Methods
Cemented total knee arthroplasty (TKA) is a widely accepted treatment for end-stage knee osteoarthritis. During this procedure, the surgeon targets proper alignment of the leg and balanced flexion/extension gaps. However, the cement layer may impact the placement of the component, leading to changes in the mechanical alignment and gap size. The goal of the study was to assess the impact of cement layer on the tibial mechanical alignment and joint gap during cemented TKA. Computer-assisted TKAs (ExactechGPS®, Blue-Ortho, Grenoble, FR) were performed by two fellowship trained orthorpaedic surgeons on five fresh-frozen non-arthritic pelvis-to-ankle cadaver legs. All the surgeries used a cemented cruciate retaining system (Optetrak Logic CR, Exactech, Gainesville, FL). After the bony resection, the proximal tibial resection plane was acquired by manually pressing an instrumented checker onto the resected tibial surface (resection plane). Once the prosthesis was implanted through standard cementing techniques, the top surface of the implanted tibial component was probed and recorded using an instrumented probe. A best fit plane was then calculated from the probed points and offset by the thickness of the prosthesis, representing the bottom plane of the component (component plane). The deviation of component alignment caused by the cement layer was calculated as the coronal and sagittal projection of the three-dimensional angle between the resection plane and the component plane. The deviation of the component height, reflecting a change in the joint gap, was assessed as the distance between the two planes calculated at the lowest points on the medial and lateral compartments of the proximal tibial surface. Statistical significance was defined as p≤0.05.INTRODUCTION
MATERIAL
Patellofemoral joint is an important aspect of the tri-compartmental knee joint complex. Total knee arthroplasty (TKA) replaces the articulating surfaces of distal femur and proximal tibia, and often times the patella as well. Understanding the size relationship between the femur and patella bones can provide valuable information for new prosthesis design and biomechanical analysis. However, taking anthropometric measurements on a large population of patients or even cadaveric specimens could be a challenge. As a result, there are currently little quantitative data existing in the literature regarding the size relationship between TKA patient's femur and patella. This study attempted to attack this question using a novel statistical approach and a large TKA patient database. A multi-site clinical database operated by Exactech was used in this study. The database contains patient information of Optetrak TKA implant recipients from over 30 physicians in US, UK, and Colombia since 1995. Nine femoral implant sizes (0, 1, 2, 2.5, 3, 3.5, 4, 5 and 6) and six patellar implant sizes (26, 29, 32, 35, 38, 41 mm) were seen in these patients. Due to the low usage, femoral sizes 0 and 6 were excluded from this analysis. Taking primary TKA only, a total of 2,698 cases were included in this study. The size relationship between femoral implant and patellar implant was analyzed in this patient population. Gender effect was also examined.Introduction
Methods
Total knee arthroplasty (TKA) is an effective technique to treat end-stage osteoarthritis of the knee. One important goal of the procedure is to restore physiological knee kinematics. However, fluoroscopy studies have consistently shown abnormal knee kinematics after TKA, which may lead to suboptimal clinical outcomes. Posterior slope of the tibial component may significantly impact the knee kinematics after TKA. There is currently no consensus about the most appropriate slope. The goal of the present study was to analyze the impact of different prosthetic slopes on the kinematics of a PCL-preserving TKA. The tested hypothesis was that the knee kinematics will be different for all tested tibial slopes. PCL-retaining TKAs (Optetrak Logic CR, Exactech, Gainesville, FL) were performed by fellowship trained orthopedic surgeons on six fresh frozen cadaver with healthy knees and intact PCL. The TKA was implanted using a computer-assisted surgical navigation system (ExactechGPS®, Blue-Ortho, Grenoble, FR). The implanted tibial baseplate was specially designed (figure 1) to allow modifying the posterior slope without repeatedly removing/assembling the tibial insert with varying posterior slopes, avoiding potential damages to the soft-tissue envelope.INTRODUCTION
MATERIAL
When evaluating the biomechanical performance of a total knee arthroplasty (TKA) implant design, device companies are usually required to select the “worst case scenario” for testing by the regulatory bodies. However, most test standards (e.g., ASTM, ISO) do not explicitly specify how the “worst case” should be determined. It is quite often that an extreme size (the smallest or the largest) in a system is taken as the “worst case” size. The smallest size is sometimes selected under the rationale that it has the smallest geometry thus the weakest mechanical structure. While the largest size is sometimes selected under the rationale that it is used on the biggest patients associated with the highest loads. However, implant geometry and in vivo load are two compounding factors that together determine the implant's biomechanical challenge. As the result, the true “worst case” must be determined considering both factors, and the choice could be design-specific. This study evaluated the femorotibial contact stress of a TKA implant system, and demonstrated that the extreme sizes may not simply be the “worst case”. The femorotibial contact stress of a posterior-stabilizing TKA implant system was assessed using finite element analysis. Multiple sizes ranging from size 0 to 6 were analyzed. For each size, the CAD models were assembled at knee extension. A load equivalent to 4 times of patient body weight was applied. Average patient body weights were calculated based on the company's clinical database: 72.5, 76.0, 80.0, 87.4, 95.2, 103.4, and 111.0 kg for sizes 0, 1, 2, 3, 4, 5 and 6, respectively. Von Mises stresses in the polyethylene tibial insert were examined and compared among different sizes.Introduction
Methods
One main perceived drawback for the adoption of computer assisted orthopaedic surgery (CAOS) during total knee arthroplasty (TKA) relates to the increased surgical time compared to the use of standard mechanical instrumentation. This study compared the time efficiency between a next generation CAOS system (ExactechGPS®, Blue-Ortho, Grenoble, FR) and conventional mechanical instrumentation, and assessed the impact of surgeon experience level on the efficiency. Surgical time was retrospectively reviewed on 63 primary TKAs performed by a board-certified orthopaedic surgeon (PP) using the Optetrak Logic® PS knee system (Exactech, Gainesville, FL), grouped as 1) Group I (control): 21 TKAs using conventional mechanical instruments; 2) Group II: 21 KAs performed using the CAOS system with an early experience level (first 21 cases); and 3) Group III: 21 TKAs using the CAOS system with an advanced experience level (beyond 30 cases). Patient condition (age, BMI, gender, etc.), surgical technique, and post-operative guidelines were similar across the three groups. No cases were lost and no patient had any intra-operative complications. Surgical time was compared across the three groups (with significance defined as p<0.05). Compared to the TKAs using conventional mechanical instrumentation, the average surgical time for the navigated TKAs performed with an early experience was 7 minutes longer. However, with an advanced experience level, the average surgical time was 2 minutes less than the time required using conventional mechanical instrument. Further, navigated TKAs with an advanced experience level exhibited the least variability among the three groups. None of the time differences were significant (p>0.20). No significant difference in TKA surgical time was found between the evaluated CAOS system (both within or pass the learning curve) and the conventional instrumentation. Nevertheless, once the learning curve was reached, the system decreased the time variability compared to conventional mechanical instrumentation. The comparable efficiency reported in this study to the conventional mechanical instrumentation may be attributed to the unique features of the ExactechGPS system, such as indication for use inside the sterile field, blood occlusion-resistant tracker design, customisable operative technique tailored to the surgeon's preference, and compact and reduced number of instruments.
Although total knee arthroplasty (TKA) is a largely successful procedure to treat end-stage knee osteoarthritis (OA), some studies have shown postoperative abnormal knee kinematics. Computer assisted orthopaedic surgery (CAOS) technology has been used to understand preoperative knee kinematics with an open joint (arthrotomy). However, limited information is available on the impact of arthrotomy on the knee kinematics. This study compared knee kinematics before and after arthrotomy to the native knee using a CAOS system. Kinematics of a healthy knee from a fresh frozen cadaver with presumably intact PCL were evaluated using a custom software application in an image-free CAOS system (ExactechGPS, Blue-Ortho, Grenoble, FR). At the beginning of the test, four metal hooks were inserted into the knee away from the joint line (one on each side of the proximal tibia and the distal femur) for the application of 50N compressive load to simulate natural knee joint. Prior to incision, one tracker was attached to each tibia and femur on the diaphysis. Intact knee kinematics were recorded using the CAOS system by performing passive range of motion 3 times. Next, a computer-assisted TKA procedure was initiated with acquisition of the anatomical landmarks. The system calculated the previously recorded kinematics within the coordinate system defined by the landmarks. The test was then repeated with closed arthrotomy, and again with open arthrotomy with patella maintained in the trochlea groove. The average femorotibial AP displacement and rotation, and HKA angle before and after knee arthrotomy were compared over the range of knee flexion. Statistical analysis (ANOVA) was performed on the data at ∼0° (5°), 30°, 60°, 90° and 120° flexion. The intact knee kinematics were found to be similar to the kinematics with closed and open arthrotomy. Differences between the three situations were found, in average, as less than 0.25° (±0.2) in HKA, 0.7mm (±0.4) in femorotibial AP displacement and 2.3° (±1.4) in femorotibial rotation. Although some statistically significant differences were found, especially in the rotation of the tibia for low and high knee flexion angles, the majority is less than 1°/mm, and therefore clinically irrelevant. This study suggested that open and closed arthrotomy do not significantly alter the kinematics compared to the native intact knee (low RMS). Maintaining the patella in the trochlea groove with an open arthrotomy allows accurate assessment of the intact knee kinematics.
