Arthrofibrosis remains a dominant post-operative complication and reason for returning to the OR following total knee arthroplasty. Trauma induced by ligament releases during TKA soft tissue balancing and soft tissue imbalance are thought to be contributing factors to arthrofibrosis, which is commonly treated by manipulation under anesthesia (MUA). We hypothesized that a robotic-assisted ligament balancing technique where the femoral component position is planned in 3D based on ligament gap data would result in lower MUA rates than a measured resection technique where the implants are planned based solely on boney alignment data and ligaments are released afterwards to achieve balance. We also aimed to determine the degree of mechanical axis deviation from neutral that resulted from the ligament balancing technique. We retrospectively reviewed 301 consecutive primary TKA cases performed by a single surgeon. The first 102 consecutive cases were performed with a femur-first measured resection technique using computer navigation. The femoral component was positioned in neutral mechanical alignment and at 3° of external rotation relative to the posterior condylar axis. The tibia was resected perpendicular to the mechanical axis and ligaments were released as required until the soft tissues were sufficiently balanced. The subsequent 199 consecutive cases were performed with a tibia-first ligament balancing technique using a robotic-assisted TKA system. The tibia was resected perpendicular to the mechanical axis, and the relative positions of the femur and tibia were recorded in extension and flexion by inserting a spacer block of appropriate height in the medial and lateral compartments. The position, rotation, and size of the femoral component was then planned in all planes such that the ligament gaps were symmetric and balanced to within 1mm (Figure 1). Bone resection values were used to define acceptable limits of implant rotation: Femoral component alignment was adjusted to within 2° of varus or valgus, and within 0–3° of external rotation relative to the posterior condyles. Component flexion, anteroposterior and proximal-distal positioning were also adjusted to achieve balance in the sagittal plane. A robotic-assisted femoral cutting guide was then used to resect the femur according to the plan (Figure 2). CPT billing codes were reviewed to determine how many patients in each group underwent post-operative MUA. Post-operative mechanical alignment was measured in a subset of 50 consecutive patients in the ligament balancing group on standing long-leg radiographs by an independent observer. Post-operative MUA rates were significantly lower in the ligament balancing group (0.5%; 1/199) than in the measured resection group (3.9%; 4/102), p=0.051. 91.3% (42/46) of knees were within 3° and 100% (46/46) were within 4° of neutral alignment to the mechanical axis post-operatively in the ligament balancing group.Methods
Results
There is increasing pressure on healthcare providers to demonstrate competitiveness in quality, patient outcomes and cost. Robotic and computer-assisted total knee arthroplasty (TKA) have been shown to be more accurate than conventional TKA, thereby potentially improving quality and outcomes, however these technologies are usually associated with longer procedural times and higher costs for hospitals. The aim of this study was to determine the surgical efficiency, learning curve and early patient satisfaction of robotic-assisted TKA with a contemporary imageless system. The first 29 robotic-assisted TKA cases performed by a single surgeon having no prior experience with computer or robotic-assisted TKA were reviewed. System time stamps were extracted from computer surgical reports to determine the time taken from the first step in the anatomical registration process, the hip center acquisition, to the end of the last bone resection, the validation of the proximal tibial resection. Additional time metrics included: a) array attachment, b) anatomical registration, c) robotic-assisted femoral resection, d) tibial resection, e) trailing, f) implant insertion, and skin-to-skin time. The Residual Time was also calculated as the skin-to-skin time minus the time taken for steps a) to f), representing the time spent on all other steps of the procedure. Patients completed surveys at 3 months to determine their overall satisfaction with their surgical joint.Introduction
Methods
Computer-assisted surgery (CAS) aims to improve component positioning and mechanical alignment in Total Knee Arthroplasty (TKA). Robotic cutting-guides have been integrated into CAS systems with the intent to improve bone-cutting precision and reduce navigation time by precisely automating the placement of the cutting-guide. The objectives of this study were to compare the intra-operative efficiency and accuracy of a robotic-assisted TKA procedure to a conventional computer-assisted TKA procedure where fixed sequential cutting-blocks are navigated free-hand. This was a retrospective study comparing two distinct cohorts: the control group consisted of patients undergoing TKA with conventional CAS (Stryker Universal Knee Navigation v3.1, Stryker Orthopaedics, MI) from May 2006 to September 2007; the study group consisted of patients undergoing TKA with a robotic cutting-guide (Apex Robotic Technology, ART, OMNIlife Science, MA) from October 2010 to May 2012. Exclusion of patients with preexisting hardware in the joint or an absence of navigation data resulted in a total of 29 patients in the control group and 52 patients in the study group. Both groups were similar with respect to BMI, age, gender, and pre-operative alignment. All patients were operated on by a single surgeon at a single institution. The navigation log files were analyzed to determine the total navigation time for each case, which was defined as the time from the start of the acquisition of the hip center to the end of the final alignment analysis for both systems. The intraoperative final mechanical axis was also recorded. The tourniquet time (time of inflation prior to incision to deflation immediately after cement hardening) and hospitalization length were compared. Linear regression analysis was performed using R statistical software v2.12.1.Introduction:
Methods:
Intimate bone-implant contact is a requirement for achieving stable component fixation and osseo-integration of porous-coated implants in TKA. However, consistently attaining a press-fit and a tight-fitting femoral component can be problematic when using conventional instrumentation. We present a new robotic cutting-guide system that permits intra-operative adjustment of the femoral resections such that a specified amount of press-fit can be consistently attained. System Description: A.R.T. (Apex Robotic Technology) employs a miniature bone-mounted robotic cutting-guide and flexible software that permits the surgeon to adjust the anterior and posterior femoral resections in increments of 0.25 mm per resection, allowing a maximum of 1.5mm of total added press in the AP dimension. The accuracy of guide-positioning and bone-cutting with A.R.T. was assessed in bench testing on synthetic bones (SAWBONES®) using an optical comparator. The individual guide locations for 16 femoral cut positioning sequences (80 guide positions in total) were measured. Femoral resections were performed with A.R.T. on eight sawbones (two per fit-adjustment setting) and the anterior-posterior dimensions of the final cut surfaces were also measured. Eight sawbones were prepared using conventional instrumentation (jigs) as controls: four with a 0 mm press-fit block and four with a +0.5 mm specially manufactured press-fit block.Introduction
Methods
We evaluated the utility of imageless computer-navigation coupled with a miniature robotic-cutting guide for managing large deformities in TKA. We asked what effect did severe pre-operative deformities have on post-operative alignment and surgery time using the system. We also report on the early functional outcomes of this group of patients. This was a retrospective cohort study of 128 TKA's performed by a single surgeon (mean age: 71y/o [range 53–93], BMI: 31.1 [20–44.3], 48males). Patients were stratified into three groups according to their pre-operative coronal plane deformity: Neutral or mild deformity <10((baseline group); Severe varus ≥10(; severe valgus ≥10(; and according to the degree of flexion contracture: Neutral or mild flexion from −5(hyperextension to 10(flexion (baseline group); hyperextension ≤−5(, and severe flexion ≥10. (The degree of deformity and final postoperative alignment achieved was measured using computer navigation in all patients and analysed using multivariate regression. The APEX CR/Ultra Knee System (OMNIlife Science, Inc.) was used with the PRAXIM Navigation system in all cases. A students t-test was used to compare pre- and post-operative (3–6 months) Knee Society Scores (KSS) and Knee Functional Scores (KSSF) for all patients.Introduction
Methods
The aim of this study was to quantify mid-flexion laxity in a total knee arthroplasty with an elevated joint line, as compared to a native knee and a TKA with joint line maintained. Our hypothesis was joint line elevation of 4mm would increase coronal plane laxity throughout mid-flexion in a pattern distinct from the preoperative knee or in a TKA with native joint line. Six fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilised implant (APEX PS, OMNIlife Science, Inc.) using a computer navigation system equipped with a robotic cutting-guide, in this controlled laboratory cadaveric study. After the initial tibial and femoral resections were performed, the flexion and extension gaps were balanced using navigation, and a 4mm recut was made in the distal femur. The remaining femoral cuts were made, the femoral component was downsized by resecting an additional 4mm of bone off the posterior condyles, and the polyethylene was increased by 4mm to create a situation of a well-balanced knee with an elevated joint line. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30, 45, 60 and 90(of flexion, when applying a standardised varus/valgus load of 9.8Nm across the knee using a 4kg spring-load located at 25cm distal to the knee joint line. Laxity was also measured in the native knee, as well as the native knee after a standard approach during TKA which included a medial release. Coronal plane laxity was defined as the absolute difference (in degrees) between the mean mechanical alignment angle obtained from applying a standardised varus and valgus stress at 0, 30, 45, 60 and 90(.Introduction
Methods
The aim of this study was to quantitatively analyze the amount coronal plane laxity in mid-flexion that occurs in a well-balanced knee with an elevated joint line of 4 mm. In the setting an elevated joint line, we hypothesized that we would observe an increased varus and/or valgus laxity throughout mid flexion. After obtaining IRB approval, nine fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilized implant (APEX PS, OMNIlife Science, Inc.) using a computer navigation system equipped with a robotic cutting-guide, in this controlled laboratory cadaveric study. After the initial tibial and femoral resections were performed, the flexion and extension gaps were balanced using navigation, and a 4 mm recut was made in the distal femur. The remaining femoral cuts were made, the femoral component was downsized by resecting an additional 4 mm of bone off the posterior condyles, and the polyethylene was increased by 4 mm to create a situation of a well-balanced knee with an elevated joint line. Real implants were used in the study to eliminate any inherent error or laxity in the trials. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30, 45, 60 and 90 degrees of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee using a 4 kg spring-load located at 25 cm distal to the knee joint line (Figure 1). Coronal plane laxity was defined as the absolute difference (in degrees) between the mean mechanical alignment angle obtained from applying a standardized varus and valgus stress at 0, 30, 45, 60 and 90 degrees. Each measurement was performed three separate times. Two tailed student t-tests were performed to analyze whether there was difference in the mean mechanical alignment angle at 0°, 30°, 45°, 60°, and 90° between the well balanced scenario and following a 4 mm joint line elevation with an otherwise well balanced knee.Introduction
Methods
The aim of this study was to quantitatively analyze the amount coronal plane laxity in mid-flexion that occurs with a loose extension gap in TKA. In the setting of a loose extension gap, we hypothesized that although full extension is achieved, a loose extension gap will ultimately lead to increased varus and/or valgus laxity throughout mid flexion. After obtaining IRB approval, six fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilized implant (APEX PS OMNIlife Science, Inc.) using a computer navigation system equipped with a robotic cutting-guide, in this controlled laboratory cadaveric study. After the initial tibial and femoral resections were performed, and the flexion and extension gaps were balanced using navigation, a 4 mm distal recut was made in the distal femur to create a loose extension gap (using the same thickness of polyethylene as the well-balanced case). Real implants were used in the study to eliminate error in any laxity inherent to the trials. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30, 45, 60 and 90 degrees of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee using a 4 kg spring-load located at 25 cm distal to the knee joint line. (Figure 1). Coronal plane laxity was defined as the absolute difference (in degrees) between the mean mechanical alignment angle obtained from applying a standardized varus and valgus stress at 0, 30, 45, 60 and 90 degrees. Each measurement was performed three separate times. Two tailed student t-tests were performed to analyze whether there was difference in the mean mechanical alignment angle at 0°, 30°, 45°, 60°, and 90° between the well balanced scenario and following a 4 mm recut in the distal femur creating a loose extension gap.Introduction
Methods
Severe angular deformities in total knee arthroplasty require specific attention to bone resections and soft tissue balancing. This can add technical complexity and time, with some authors reporting an increase of approximately 20 minutes in mean surgery time when managing large deformities with conventional instrumentation [1]. We evaluate the utility of computer-navigation with imageless BoneMorphing® and Apex Robotic Technology, or A.R.T.® for managing large deformities in TKA. BoneMorphing® allows for real-time visualization of virtual bone resection contours, limb alignment and soft-tissue balance during TKA. A.R.T. permits accurate cutting and recutting of the distal femur in 1 mm increments. We asked what effects do severe pre-operative deformities have on post-operative alignment and surgery time in comparison to knees with only mild deformities when using this system. This was a retrospective cohort study of 128 consecutive A.R.T. TKA's performed by a single surgeon (mean age: 71 y/o [range 53–93], BMI: 31.1 [20–44.3], 48 males). Patients were stratified into three groups according to their pre-operative coronal plane deformity: Neutral or mild deformity <10° (baseline group); Severe varus ≥10°; and Severe valgus ≥10°; and according to the degree of flexion contracture: Neutral or mild flexion from −5° hyperextension to 10° flexion (baseline group); Hyperextension ≤−5°, and Severe flexion ≥10°. The degree of deformity and final postoperative alignment achieved was measured using computer navigation in all patients and analyzed using multivariate regression. The APEX CR/Ultra Knee System (OMNIlife Science, Inc.) was used in all cases.Introduction
Methods
Long-term implant survivorship in total knee arthroplasty (TKA) depends on the alignment of the tibial and femoral components, as well as on the mechanical alignment of the leg. Computer navigation improves component and limb alignment in TKA compared to the manual technique. However, its use is often associated with an increase in surgical time. We aimed to evaluate the use of adjustable cutting blocks (ACB) in navigated TKA. We hypothesised that the use of ACB would (1) improve tibial and femoral component positioning; (2) improve postoperative mechanical leg alignment; and (3) decrease tourniquet time, when compared to conventional cutting blocks (CCB). This was a retrospective cohort study of 94 navigated primary TKA. Patients were classified into two groups according to whether the surgery had been performed using ACB or CCB. There were sixty-four patients in the CCB group and 30 patients in the ACB group. Charts were reviewed to obtain the following data: age, gender, body mass index (BMI), tourniquet time and operated side. Pre- and postoperative standing full-leg radiographs and lateral radiographs were reviewed. Mean coronal femoral alignment for the CCB group was 0.8® varus (SD = 1.95®) and for the ACB group it was 1.1® varus (SD = 1.5®) (P = 0.12). Mean coronal tibial alignment for the CCB group was 0.1® valgus (SD = 1.3®) and for the ACB group it was 0.5® varus (SD = 1.01) (P = 0.15). Sagittal tibial alignment was a mean 0.5® of anterior slope (SD = 2.9®) for the CCB group and 0.7® anterior slope (SD = 2.5®) for the ACB group (P = 0.38). Preoperatively, the CCB group had a mean mechanical alignment of 1.8® varus (SD = 9.6®), while the ACB group had a mean 1.8® varus (SD = 9.37®) (P = 0.88). After surgery, mechanical leg alignment for the CCB group improved to a mean 0.7® varus (SD = 2.7®) (P = 0.0001), while the ACB group improved to 1.8® varus (SD = 1.7®) (P<0.0001). There was significantly less variability in postoperative mechanical alignment in the ACB group (P = 0.0091). Mean tourniquet time for the CCB group was 91 minutes (SD = 17.7 minutes). The ACB group a mean tourniquet time of 76 minutes (SD = 16.7 minutes) (P = 0.01). In the multiple linear regression model, the use of an ACB reduced tourniquet time by 16.8 minutes (P = 0.001). Adjustable cutting blocks for TKA significantly reduced postoperative mechanical alignment variability and tourniquet time compared to conventional navigated instrumentation, while providing equal or better component alignment.
Accurate and reliable registration of the ankle center is a necessary requirement in computer-assisted TKR. There is debate among surgeons over which registration procedure more accurately reflects the true center of the ankle joint. The aim of this study was to compare two different ankle registration landmarks on radiographs and determine how much they differed from the anatomic center of the talus in the frontal plane. Specifically, we asked what the average deviation in tibial mechanical axis registration would be when registering the ankle center using: A) the extreme medial and lateral points; and B) the most distal points, of the respective malleoli. A second question was whether or not BMI had any significant effect on mechanical axis registration error. We reviewed the preoperative hip-to-ankle radiographs of 40 patients who underwent navigated TKR at our institution. The patient cohort was composed of 32 females and 7 males, with a mean age of 69 years (range, 45–84 years) and a mean BMI of 29.9 (range, 14.7–43.3). All radiographs were stored in and reviewed using PACS. No clinically significant divergence from the anatomic center of the ankle was seen when using the Extremes Midpoint technique (mean divergence = 0.2® lateral; SD = 0.5®; 95% CI = −0.3®, −0.1®) or the Distal Midpoint technique (mean divergence = 0.2® lateral; SD = 0.6®; 95% CI = −0.39®, 0®). The mean difference between both techniques was 0.02® (SD = 0.3®; 95% CI = −0.1®, 0.1®; P = 0.68). BMI had no significant effect on the divergence from the true ankle center for either the Extremes Midpoint (R2 = 0.002; P = 0.78) or the Distal Midpoint techniques (R2 = 0.004; P = 0.90).(Figure 2) The center of the ankle, as determined by using the Extremes Midpoint technique, lied 1.1 mm (SD = 2.6 mm; 95% CI = −1.9 mm to −0.3 mm) from the anatomic axis of the tibia. When determined using the Distal Midpoint technique, the center of the ankle lied 1.7 mm (SD = 2.3 mm; 95% CI = −2.5 mm to −0.98 mm) from the anatomic axis. Although statistically significant (P = 0.028), this difference was not clinically relevant (<3 mm). BMI had no significant effect on these differences (R2 = 0.07; P = 0.11; R2 = 0.02, P = 0.38).(Figure 3) There is no significant difference between ankle registration using the Extremes Midpoint or the Distal Midpoint techniques and the anatomic center of the ankle. Patients' BMI does not seem to affect the registration of the ankle center with either technique.
Robotic-guided arthroplasty procedures are becoming increasingly common. We introduced a new computer-navigated TKA system with a robotic cutting-guide into a community-based hospital and characterized the accuracy and efficiency of the technique. We retrospectively reviewed our first 100 cases following IRB approval. Tourniquet time, intraoperative bone-cut accuracy and final limb alignment as measured by the computer were collected and divided into consecutive quartiles: Groups I, II, III, and IV; 25 cases per group. All resections were planned neutral to the mechanical axis. Postoperative component alignment and overall mechanical axis limb alignment were also measured on standing long-leg radiographs by two independent observers at minimum six weeks follow-up. Radiographic alignment was available for 62 cases.
Imageless computer-navigated TKA with a robotic cutting guide allowed one surgeon to make bone resections within 3° of neutral in 98% of cases. Radiographic limb alignment was less precise, which is consistent with the known limitations inherent to this measurement technique. Surgeons can expect this procedure to take 15 additional minutes during the first ten cases and five additional minutes during the second ten cases on average, without compromising accuracy.
Robotic-guided arthroplasty procedures are becoming increasingly common, though to our knowledge there are no published studies on robotic cutting guides in TKA. We introduced a new computer-navigated TKA system with a robotic cutting-guide into a community-based hospital and characterized the accuracy and efficiency of the technique with respect to bone cutting, component alignment and final limb alignment, and tourniquet time. The first 100 cases from a single-surgeon were retrospectively reviewed following IRB approval. Intra-operative bone-cut accuracy and overall limb alignment as measured by the computer were collected and divided into consecutive quartiles: Group I, cases 1–25; Group II, cases 26–50; Group III, cases 51–74; Group IV, cases 75–100. All resections were planned neutral to the mechanical axis. Postoperative component alignment and the overall mechanical axis limb alignment in the coronal plane were also measured on standing long-leg AP radiographs by two independent observers at a minimum six weeks post-op. This mechanical radiographic alignment was available for 62 cases. Tourniquet time (the time prior to incision until after cementation) and robotic cutting guide use time were also analyzed.Introduction
Methods
The aims of this study were: 1) to quantitatively analyse the amount of knee extension that is achieved with +2mm incremental increases in the amount of distal femoral bone that is resected during TKA in the setting of a flexion contracture, 2) to quantify the amount of coronal plane laxity that occurs with each 2mm increase in the amount of distal femur resected. In the setting of a soft tissue flexion contracture, we hypothesized that although resecting more distal femur will reliably improve maximal knee extension, it will ultimately lead to increased varus and/or valgus laxity throughout mid-flexion. Seven fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilized implant using a measured resection technique with computer navigation system equipped with a robotic cutting-guide, in this IRB approved, controlled laboratory study. After the initial tibial and femoral resections were performed, the posterior joint capsule was sutured (imbricated) through the joint space under direct visualization until a 10° flexion contracture was obtained with the trial components in place, as confirmed by computer navigation. Two distal femoral recuts of +2mm each where then subsequently made and after the remaining femoral cuts were made, the trail implants were reinserted. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30°, 60° and 90° of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee using a 4kg spring-load located at 25cm distal to the knee joint line.(Figure 1) Coronal plane laxity was defined as the absolute difference (in °) between the mean mechanical alignment angle obtained from applying a standardized varus and valgus stress at 0°, 30, 60° and 90°. Each measurement was performed three separate times and averaged. The maximal extension angle achieved following each 2mm distal recut was also recorded. Two-tailed student's t-tests were performed to analyze whether there was difference in the mean laxity at each angle and if there was a significant improvement in maximal extension with each recut. P-values < 0.05 were considered significant.Aims/Hypothesis
Methods
Our aim was to compare the passive kinematics and coronal plane stability throughout flexion in the native and the replaced knee, using three different TKA designs: posterior stabilized (PS), bi-cruciate substituting (BCS), and ultracongruent (UC). Our hypotheses were: 1.) a guided motion knee replacement (BCS) offers the closest replication of native knee kinematics in terms of femoral rollback 2.) the replaced knee will be significantly more stable in the coronal plane than the native knee; 3.) No difference exists in coronal plane stability between the 3 implants/designs throughout flexion. After IRB approval, two cadaveric specimens were used for a pilot study to determine sample size. Five fresh-frozen hip-to-toe cadaveric specimens then underwent TKA using an anatomic measured resection technique with a computer-navigated robotic femoral cutting-guide. The PS, BCS, and UC TKA designs were implanted in each knee using the same distal and posterior femoral cuts to standardize the position of the implants. Computer navigation was then utilized to record the varus/valgus laxity of each implant at 0°, 30°, 60° and 90° of flexion while applying a standardized 9.8Nm moment. Passive tibiofemoral kinematics were measured in a continuous passive motion machine from 10° to 110°. Femoral rollback on the tibia was calculated for the native and replaced knees by measuring the closest point (CP) on the femoral condyle to a transverse plane perpendicular to the mechanical axis of the tibia at each flexion angle.Purpose
Methods
the mean medial gap was 1.5–2.5mm smaller than the mean lateral gap for all scenarios and forces tested (p<
0.05); everting the patella decreased the medial and lateral gaps by 1mm and 1.3mm with an intact PCL, and by 1mm and 2.7mm with the PCL resected, respectively; PCL resection resulted in increased flexion gap heights of ~1–2mm for both sides. During knee flexion from 30° to 90°, the PCL tended to squeeze the medial compartment by 1–2mm (p<
0.05). Increasing the force from 50N to 100N per side resulted in a mean gap increase of 0.5mm throughout the range of flexion.
