Faculty Bibliography

Background/UNASSIGNED:There is a paucity of literature assessing whether payer type has an impact on postoperative patient-reported outcomes (PROs) after total knee arthroplasty (TKA). The aim of this study was to comparatively evaluate TKA PROs among patients with commercial and Medicare insurance. Methods/UNASSIGNED:We conducted a single-center, retrospective review of patients operated between January 2017 and March 2018. Knee Disability and Osteoarthritis Outcome Score Junior (KOOS-Jr) and Veterans RAND 12 Health Survey (VR-12) Physical Component (VR-12 PCS) and Mental Component (VR-12 MCS) PRO scores were collected prospectively at baseline and 12 weeks postoperatively via an electronic patient rehabilitation application. Univariable and multivariable linear regressions were utilized to assess the effects of patient insurance type on PRO. Results/UNASSIGNED:> .05). Conclusions/UNASSIGNED:After adjusting for patient-specific variables, PROs are similar at baseline and 12 weeks postoperatively between commercial and Medicare cohorts. For TKA candidates with similar baseline demographics, surgeons can expect similar perioperative PROs regardless of insurance type.

Background and Aims: Successful total knee replacement (TKA) is dependent on balancing peak load at the medial and lateral tibiofemoral joint interfaces. This can be achieved using a sterile sensor system intra-operatively. On the request of one surgeon at our institution, we explored the feasibility and safety of spinal anesthesia with limited motor blockade. Methods: 25 patients were enrolled in an IRB-approved non-randomized pilot study. For spinal anesthesia, a solution consisting of 1 mL of 5 mg/mL isobaric bupivacaine with 1.5 mL sterile saline solution containing 7.5 mcg of sufentanil was administered. During surgery, after components were cemented, patients were awakened and asked to move their leg in order to measure pressure balance. If an imbalance was noted, the surgeon would make adjustments intraoperatively. Results: During the intraoperativewake-up test, 15 patients successfully flexed and extended at the knee on command, while 10 were too weak for meaningful testing. As we reduced the local anesthetic volume to 0.8 mL in patients shorter than 160 cm, that issue was eliminated. One patient had neutral recollection of the test on follow up. No patient had pain or other side effect. Conclusions: A spinal anesthetic using sufentanil in combination with lowdose local anesthetic appears feasible and safe to provide surgical anesthesia for TKA. By performing a motor-sparing spinal anesthetic with an intraoperativewake up test, we can allow surgeons to test active pressure balance to improve the accuracy of the pressure balancing technique. A randomized study is in preparation to determine whether long-term surgical result is improved

Introduction/objectives: Computer-assisted hip navigation offers the potential for more accurate placement of hip components, which is important in avoiding dislocation, impingement, and edge-loading. The purpose of this study was to determine if the use of computer-assisted hip navigation reduced the rate of dislocation in patients undergoing revision THA. Methods: We retrospectively reviewed 72 patients who underwent computer-navigated revision THA between January 2015 and December 2016. Demographic variables, indication for revision, type of procedure, and postoperative complications were collected for all patients. Clinical follow-up was performed at 3 months, 1 year, and 2 years. Results: All 72 patients (48% female; 52% male) were included in the final analysis. Mean age of patients undergoing revision THA was 70.4, mean BMI was 26.4 +/- 5.2 kg/m2. The most common indications for revision THA were instability (31%), aseptic loosening (29%), osteolysis/ eccentric wear (18%), infection (11%), and miscellaneous (11%). During revision procedure, polyethylene component was most commonly changed (46%), followed by femoral head (39%), and acetabular component (15%). At final follow-up, there were no dislocations among all study patients (0%). Compared to preoperative dislocation values, there was a significant reduction in the rate of dislocation with the use of computer- assisted hip navigation (31% vs. 0%; p<0.05). Conclusion: Our study demonstrates a significant reduction in the rate of dislocation following revision THA with the use of computer navigation. Although the cause of postoperative dislocation is often multifactorial, the use of computer- assisted surgery may help to curtail femoral and acetabular malalignment in revision THA

BACKGROUND:Total knee designs that attempt to reproduce more physiological knee kinematics are gaining attention given their possible improvement in functional outcomes. This study examined if a total knee designed for anatomic motion, where the soft tissue balancing was intended to replicate anatomical tibiofemoral contact forces, can more closely reproduce the laxity of the native knee. METHODS:In an ex-vivo setting, the laxity envelope of the knees from nine lower extremity specimens was measured using a rig that reproduced surgical conditions. The rig allowed application of a constant varus/valgus (V/V) and internal-external (I/E) torque through the range of motion. After testing the native knee, total knee arthroplasty (TKA) was performed using the Journey II bi-cruciate substituting implant. Soft tissue balancing was guided by targeting anatomical compressive forces in the lateral and medial tibiofemoral joints with an instrumented tibial trial. After TKA surgery, the laxity tests were repeated and compared to the native condition. RESULTS:The TKA knee closely reproduced the coronal laxity of the native knee, except for a difference at 90° of flexion for valgus laxity. Looking at the rotational laxity, the implant constrained the internal rotation relative to the native knee at 45 and 60° of flexion. The forces on the tibial trial for the neutral path of motion showed higher values on the medial side as the knee flexed. CONCLUSIONS:This study suggested that when using an anatomically-designed knee, the soft tissue balancing should also aim for anatomical contact forces, which will result in close to normal laxity patterns.

Proper tension of the knee's soft tissue envelope is important during total knee arthroplasty; incorrect tensioning potentially leads to joint stiffness or instability. The latter remains an important trigger for revision surgery. The use of sensors quantifying the intra-articular loads, allows surgeons to assess the ligament tension at the time of surgery. However, realistic target values are missing. In the framework of this paper, eight non-arthritic cadaveric specimens were tested and the intra-articular loads transferred by the medial and lateral compartment were measured using custom sensor modules. These modules were inserted below the articulating surfaces of the proximal tibia, with the specimens mounted on a test setup that mimics surgical conditions. For both compartments, the highest loads are observed in full extension. While creating knee flexion by lifting the femur and flexing the hip, mean values (standard deviation) of 114N (71N) and 63N (28N) are observed at 0 degrees flexion for the medial and lateral compartment respectively. Upon flexion, both medial and lateral loads decrease with mean values at 90 degrees flexion of 30N (22N) and 6N (5N) respectively. The majority of the load is transmitted through the medial compartment. These observations are linked to the deformation of the medial and lateral collaterals, in addition to the anatomy of the passive soft tissues surrounding the knee. In conclusion, these findings provide tangible clinical guidance in assessing the soft tissue loads when dealing with anatomically designed total knee implants.

BACKGROUND: To our knowledge, no study has assessed the ability of rigid patient positioning devices to afford arthroplasty surgeons with ideal acetabular orientation throughout surgery. The purpose of this study is to use robotic arm-assisted computer navigation to assess the reliability of pelvic position in total hip arthroplasty performed on patients positioned with rigid positioning devices. METHODS: A prospective cohort of 100 hips (94 patients) underwent robotic-guided total hip arthroplasty in the lateral decubitus position from the posterior approach, 77 stabilized by universal lateral positioner, and 23 by peg board. Before reaming, computed tomography-templated computer software generated true values of pelvic anteversion and inclination based on the position of the robot arm registered to the patient's preoperative pelvic computed tomography. RESULTS: Mean alteration in anteversion and inclination values was 1.7 degrees (absolute value, 5.3 degrees ; range, -20 degrees to 20 degrees ) and 1.6 degrees (absolute value, 2.6 degrees ; range, -8 degrees to 10 degrees ), respectively. And 22% of anteversion values were altered by >10 degrees and 41% by >5 degrees . There was no difference between hip positioners used (P = .36). Anteversion variability was correlated with body mass index (P = .02). CONCLUSION: Despite the use of rigid patient positioning devices-a lateral hip positioner or peg board-this study reveals clinically important malposition of the pelvis in many cases, especially with regard to anteversion. These results show a clear need to pay particular attention to anatomic landmarks or computer-assisted techniques to assure accurate acetabular cup positioning. Patient positioning should not be solely trusted.

Introduction/objectives: Computer/robotic navigation has been shown to improve the precision of acetabular component position in THA. The purpose of our study was to utilize robotic-arm assisted computer navigation to assess the reliability of pelvic position in total hip arthroplasty, which can directly impact anteversion and inclination. Methods: 100 hips underwent a CT-guided robotic THA via a minimally invasive posterior approach in the lateral position. The surgeon placed the robotic arm parallel to the longitudinal axis of the patient and the horizontal surface of the table, representing 0 degrees anteversion and inclination. The software generated values of this perceived zero-zero position based on the registration of the patient's preoperative CT. To ensure the accuracy of measurements, cup anteversion and inclination at time of impaction were recorded and compared to 3 month postop X-rays. Results: 22% of anteversion values were altered by >10 degrees and 41% of anteversion values were altered by >5 degrees. Range of anteversion was-20 to 20 degrees. 2% of inclination values were altered by >10 degrees. 18% of inclination values were altered by >5 degrees. Anteversion differences were correlated with patient BMI (p = 0.02). There was no difference in robotic planned anteversion and inclination compared to postoperative X-rays (21.8 vs 21.9 degrees anteversion; 40.6 vs 40.5 degrees inclination). Conclusions: Pelvic positioning devices offer up to 20 degrees of variability in acetabular cup orientation. Compounding this with the fact that human error is prone to 10 degrees of anteversion inaccuracy, it is essential to ensure accurate patient position or use some form of computer/robotic navigation to place acetabular components within the well defined safe zones

BACKGROUND: Balancing is an important part of a total knee procedure, and in recent years, more emphasis has been given to quantifying the process. METHODS: During 101 total knee surgeries, initial bone cuts were made using navigation. Lateral and medial contact forces were determined throughout flexion using an instrumented tibial trial. Balancing was defined as a ratio of the medial and total force, the target being 0.5 (equal lateral and medial forces). Based on the initial values, surgical corrections were selected to achieve balancing. The most common corrections were soft tissue releases (63 incidences), including MCL, posterolateral corner, posteromedial corner, and changing tibial insert thicknesses (34 incidences). RESULTS: After final balancing, the mean ratio was 0.52 +/- 0.14, between 0.35 and 0.65 being achieved in 80% of cases. In 84% of cases, only 0-2 corrections were required. The average total force on the condyles was 215 +/- 86 N. CONCLUSION: Our study provides data to surgeons on the results to expect when balancing a knee, which can enhance both accuracy and consistency of the procedure.

INTRODUCTION: So far little is still known regarding a relationship between the laxity and forces on the medial and lateral plateau during TKA surgery. Knowing this relationship, together with the laxity envelope of the knee before and after surgery could give useful information to the surgeon when performing TKA. The first aim of this study is to compare the laxity envelope of a native knee with the knee after TKA surgery. The second aim is to examine the correlation between the knee laxity and contact forces on the tibial plateau after the surgery. It is hypothesized that the varus and valgus (VV) laxity will be inversely proportionate to the lateral and medial contact forces respectively, during the neutral path of motion. METHODS: A special rig that reproduced surgical conditions and fit onto an operating table was designed. The femur is constrained to flexion-extension about the femoral head center, while the tibia is left unconstrained in 5 degrees of freedom. The foot is mounted on bearings which allow medial-lateral translation during a heel-push flexion-extension test [1]. The rig allows to apply a constant varus/valgus moment and to control the internal/external (IE) torque. In this study a VV of 1 ONm and IE torque of 2 Nm were considered. Eight non-arthritic half semi-body hip to toe cadaveric specimens were used in this preliminary study. A series of heel push and thigh pull tests under different loading combination were performed. Neutral path of motion is considered as a heel-push flexion-extension test with no external VV and IE load applied [1]. The flexion angle, the varus-valgus angle and the internal-external rotation angle were measured using a navigation system. After testing the native knee, a total knee arthroplasty was performed by an experienced surgeon (PAM) using the Journey II BCS implant. Compressive forces on the lateral and medial condyle were measured with an instrumented tibial trial (Orthosensors, Dania Beach, Florida). After the procedure, the tests were repeated with the trial sensor inside and the laxity and the contact forces on the tibial plateau were recorded. RESULTS: Three specimens were used for method development. The results for two specimens are shown in Fig 1-3. In the intact condition both specimens showed a similar trend for VV laxity; the laxity generally increased with increasing flexion angle. On the other hand, the internal-external (IE) rotational laxity in the native knee is higher in the mid-range of flexion. After TKA surgery there is increased VV laxity in both specimens over the entire range of motion. Differences of less than 5 degrees were noticed between 45 and 100 degrees, while both specimens displayed more disparity in early flexion (Fig.l-A). The IE rotational laxity after surgery decreased for the first specimen and increased for the second. Differences of less than 5 degrees in the mid-range of flexion (30-80 degrees) were noticed, while in full extension and beyond 90 degrees of flexion, differences reached up to 10 degrees (Fig.l-B). No inverse relationship between medial load and varus angle and lateral load and valgus angle was seen in the first specimen (Fig 2). For specimen two, however as the knee flexed from 60 degrees into high flexion, the varus angle increased gradually to 7 degrees, and the medial force also gradually increased of 30 lbs (Fig.3-red square). DISCUSSION: Gathering a laxity envelope for a native knee during surgical conditions can provide important information for the balancing of the knee at surgery. To obtain optimal outcome for surgical balance and improve patient satisfaction we believe that, not only the pressure on the medial and lateral plateau should be considered, but the laxity envelope and the neutral path could be of equal importance, resulting in guidance for a surgeon during the operation. Furthermore, if a relationship between forces and laxity exists the surgeon could aim to reproduce the native laxity envelope with just the use of an instrumented tibial trial. Preliminary results show that differences in the laxity envelope in the mid-range of flexion are less than 5 degrees for both IE and VV, while both increase in full extension and full flexion. This is due to the changes in forces on the tibial plateau after surgery, since higher load would lead to interlocking between the tibia and the femur reducing the laxity [2]. Even though a statistical significance could not be established yet due to the amount of specimen analyzed, a relationship between varus-valgus laxity and medial-lateral force during neutral-path of motion is noted in the second knee, this could be due to the lift off of the lateral side beyond 75 degrees of knee flexion that led to increase pressure on the medial side. SIGNIFICANCE: Differences in laxity envelope before and after surgery measured mimicking a surgical environment could be of significant importance for performing TKA surgery. Knowing a relationship between the contact forces at surgery and the laxity envelope could increase the chance of optimal surgical outcome while balancing at surgery