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
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.
Total knee arthroplasty (TKA) is a common procedure with good success rates. The literature shows resection accuracy plays a crucial role in device longevity1. Computer guidance is used by some surgeons to enhance accuracy. This study reports on a continuous series of Optetrak knee prostheses (Exactech Inc., FL, USA) implanted by three senior surgeons between October 2010 and December 2013. 324 TKA were implanted at the Joseph Ducuing Hospital, Toulouse, France (Site 1), the Cleveland Clinic, Cleveland, OH, USA (Site 2) and the Riverview Hospital, Noblesville, IN, USA (Site 3) using Exactech GPS (Blue-Ortho, Grenoble, FR), a new computer-assisted guidance system. Each centre in this study used different surgical profiles defined specifically for their surgeical preferences. Planned tibial and femoral cuts were compared to actual cuts digitised using GPS. Operating time was analyzed and post-operative leg alignment was compared to pre-operative. The mean error between planned and digitised proximal tibial cuts was 0.06°±0.89 of valgus and 0.53°±0.90 of anterior slope for Site 1, 0.18°±0.85 of varus and 0.25°±1.18 of posterior slope for Site 2, and 0.02°±0.51 of valgus and 0.60°±1.15 of anterior slope for Site 3. The mean error between planned and digitised femoral distal cuts was 0.14°±0.85 of valgus and 0.49°±0.93 of flexion for Site 1, 0.15°±0.96 of varus and 0.04°±1.54 of extension for Site 2, and 0.09°±0.54 of varus and 0.48°±1.21 of extension for Site 3. Average operating time was 29 minutes for Site 1, 39 minutes for Site 2, and 33 minutes for Site 3. Post-operative Hip-Knee-Ankle angle (HKA) varied between 172° and 184° with an average of 179° for Site 1, 177° to 183° with an average of 179° for Site 2, and 177° to 185° with an average of 180° for Site 3. Pre-operative HKA ranged from 162 to 189°. Site 1 was already reporting in the series presented at ISTA 20132. Sites 2 and 3 were added later and could therefore benefit from the early feedback the analysis of site 1 cases provided. The use of the computer guidance at the new sites was associated with promising results and it did not take long to the surgeons to reach a reproducibility equivalent to the one of site 1. Average surgical time was similar in all three sites. GPS guidance added an average of 10 minutes to standard surgical times. All surgeons agreed the increased accuracy justified the additional time. Average post-operative HKA was 179°. HKA scores were within 3° of perfect alignment in 96% of the cases of Site 1, 99% of Site 2 and 97% of Site 3. According to the literature1, HKA between 177° and 183° is linked with high implant survival. Participating surgeons still associated Exactech GPS with satisfactory immediate post-operative results.
Total knee arthroplasty (TKA) is a common procedure with good success rates. The literature shows resection accuracy plays a crucial role in device longevity1. Computer guidance is used by some surgeons to enhance accuracy. This study reports on a continuous series of Optetrak knee prostheses (Exactech Inc., FL, USA) implanted by three senior surgeons between July 2010 and April 2013. 259 TKA were implanted at the Haguenau Hospital, Haguenau, France (Site 1), Joseph Ducuing Hospital, Toulouse, France (Site 2) and Saint Michaels Medical Center, Newark, NJ, USA (Site 3) using Exactech GPS (Blue-Ortho, Grenoble, FR), a new computer-assisted guidance system. Surgeons can use the unique Exactech GPS profiler to define steps to be computer-assisted during surgery. Each centre in this study used different surgical profiles. Planned tibial and femoral cuts were compared to actual cuts digitised using GPS. Operating time and external femoral rotation were analyzed and post-operative leg alignment was compared to pre-operative. The mean error between planned and digitised proximal tibial cuts was 0.26° ± 1.11 of valgus and 0.06° ± 0.99 of posterior slope for Site 1, 0.07° ± 0.89 of varus and 0.53° ± 0.90 of anterior slope for Site 2, and 0.19° ± 0.73 of varus and 0.10° ± 1.17 of posterior slope for Site 3 (see Fig. 1). The mean error between planned and digitised femoral distal cuts was 0.03° ± 0.99 of varus and 0.67° ± 1.36 of extension for Site 1, 0.14° ± 0.85 of varus and 0.49° ± 0.94 of extension for Site 2, and 0.26° ± 0.86 of varus and 0.09° ± 1.22 of flexion for Site 3. Average operating time was 38 minutes for Site 1, 29 minutes for Site 2, and 34 minutes for Site 3. External femoral component rotation ranged from 0° to 18° with an average of 3.7° degrees for Site 1 and from −3° to 8° with an average of 3.0° for Site 2. External rotation was fixed at 3° for Site 3. Post-operative Hip-Knee-Ankle angle (HKA) varied between 177° and 182° with an average of 179° for Site 1, 172° to 184° with an average of 179° for Site 2, and 178° to 185° with an average of 180° for Site 3. Pre-operative HKA ranged from 162 to 191°. Despite different techniques and teams, all surgeons experienced similar results. Cuts were aligned in the frontal plane, while guidance was harder to follow in the sagittal plane, possibly due to saw blade bending during resection. Average surgical time was similar. GPS guidance added an average of 10 minutes to standard surgical times. All surgeons agreed the increased accuracy justified the additional time. Regardless the site, all average femoral rotations were close to the accepted 3° standard. Average post-operative HKA was 179°. HKA scores were within 3° of perfect alignment in all Site 1 cases and 96% of Site 2 and Site 3 cases. According to the literature1, HKA between 177° and 183° is linked with high implant survival. Participating surgeons associated Exactech GPS with satisfactory immediate post-operative results.
