Faculty Bibliography

BACKGROUND:Soft tissue balancing is integral in providing stability following total knee arthroplasty (TKA). Although intraoperative contact load sensors are providing insights into the effects of soft tissue balancing, there is still a lack of understanding of the relationship between the knee's ligamentous tensions and joint surface contact loads. This study reports on the development of a multifunctional testing apparatus that can quantify the effects of ligamentous tension on joint contact loads in a controlled repeatable environment. METHODS:The functional knee apparatus was constructed to act as an anatomical substitute for the benchtop assessment of intraoperative soft tissue balancing. The system was calibrated through reproduction of results from a cadaveric study that employed intraoperative load sensors. Experimentation was then conducted to quantify the effects of tensile pretension variation on measured contact loads throughout the full range of flexion. RESULTS:A linear relationship between the ligamentous tensions and contact loads was observed, with ligaments contributing to 74-80% of the measured contact loads. Ligamentous tensions could be approximated from measured contact loads to within ± 23 N. CONCLUSION/CONCLUSIONS:The proposed apparatus can prove to be a valuable tool in the continued exploration of currently undocumented effects (e.g. surgical alteration) in soft tissue balancing. In addition to quantifying the relationship between ligamentous tensions and joint contact loads, soft tissue loading conditions where bicondylar contact was lost (i.e. known sign of kinematic instability) were identified. As a corollary, this system may be able to provide insights on soft tissue balancing standards predictive of patient outcomes.

Total joint arthroplasty (TJA) is one of the most performed and successful surgeries in the United States for advanced degenerative and inflammatory arthritis with most patients reporting excellent outcomes. However, a large number of patients are still dissatisfied following TJA. To improve outcomes, new technologies such as patient-specific instrumentation and custom implants; smart implant trials; radiologic, computer, and portable accelerometer-based navigation systems; and robotics have been developed. Their overall goals are to avoid the drawbacks of conventional arthroplasty surgery, to simplify the procedures, to improve the accuracy of surgical techniques, to improve outcomes, and to decrease costs. This chapter provides an overview of the current technologies and their applications in TJA.

BACKGROUND:The 2013 American Academy of Orthopedic Surgeons evidence-based guidelines recommend against the use of preoperative narcotics in the management of symptomatic osteoarthritic knees; however, the guidelines strongly recommend tramadol in this patient population. To our knowledge, no study to date has evaluated outcomes in patients who use tramadol exclusively as compared with narcotics naive patients. METHODS:This is a retrospective study of prospectively collected data for patients who underwent unilateral primary total knee arthroplasty between January 2017 and March 2018. PRO scores were obtained using a novel electronic patient rehabilitation application, which pushed PRO surveys via email and mobile devices within 1 month prior to surgery and 3 months postoperatively. RESULTS:One hundred and thirty-six patients were opiate naïve, while 63 had obtained narcotics before the index operation. Of those, 21 patients received tramadol. The average preoperative Knee Disability and Osteoarthritis Outcome Scores were 50.4, 49.95, and 48.01 for the naïve, tramadol, and narcotic populations, respectively, (P = .60). The tramadol cohort had the least gain in 3 months postoperative Knee Disability and Osteoarthritis Outcome Scores, improving on average 12.5 points in comparison to the 19.1 and 20.1 improvements seen in the narcotic and naïve cohorts, respectively (P = .09). This difference was statistically significant when comparing the naïve and tramadol populations alone in post hoc analysis (P = .016). CONCLUSIONS:When comparing patients who took tramadol preoperatively to patients who were opiate naïve, patients that used tramadol trended toward significantly less improvement in functional outcomes in the short-term postoperative period.

BACKGROUND:Spacer blocks, tensors, or instrumented tibial trials are current methods of balancing the knee during surgery but there are no current techniques for measuring ligament forces. Our goal was to study the relationship between the collateral ligament forces and the condylar contact forces to determine whether there was equivalence. METHODS:A test rig was constructed modeling an artificial knee joint with collateral ligaments. The ligament forces as well as the lateral and medial tibial contact forces were measured during flexion for different positions of the femoral component on the femur, producing a set of forces for the simulated conditions. A regression analysis was used to study the correlation between the ligament and contact forces. RESULTS:The combined medial and lateral ligament and contact forces showed a linear relation with a correlation coefficient of 0.98. For the medial and lateral sides separately, the correlations were 0.85 and 0.88, respectively, with more than 80% of points within a ±25% deviation from the linear relations. This deviation from the linear correlation is linked to differences in medial-lateral femoral-tibial contact point locations at different flexion angles. CONCLUSION/CONCLUSIONS:Within balancing accuracies generally achieved at surgery, the collateral ligament forces were linearly correlated to the condylar contact forces. These forces can also be equally correlated to the distraction forces as well as the moments at which condylar liftoff would occur from varus-valgus moments. This indicated a unification of the different balancing parameters, and hence such quantitative methods can be used interchangeably.

Background/UNASSIGNED:The purpose of the study was to investigate the accuracy of balancing which could be achieved at total knee surgery and its relation to functional outcomes. Methods/UNASSIGNED:During surgery, the forces on the medial and lateral plateaus were measured at 10-15 degrees flexion in 101 patients, using an instrumented tibial trial, with equal forces being targeted. Of the initial 101 cases, 71 cases completed all follow-up visits to 1 year. At each follow-up visit, the function was measured using the Knee Society Scoring System, and varus and valgus laxity angles were measured. Results/UNASSIGNED:The mean medial/(medial + lateral) compartmental force ratio was 0.52, with a standard deviation of 0.09. The total contact force was 217 Newtons, with a standard deviation of 72 Newtons. No correlations were found between the functional scores and the compartmental force ratio or total contact force. However, the mean varus and valgus laxity angles, 2.8 and 2.3 degrees, respectively, were very close to the angles of normal intact knees. Conclusions/UNASSIGNED:The likely reason for the lack of correlation of function was that the large majority of the balancing ratios were within the range 0.4-0.6 but with a wide spread of functional scores typical of total knee study groups. However, the normal varus and valgus angles achieved at follow-up indicated that equal balancing in early flexion was a reasonable surgical target. Using instrumented tibial trials enabled accurate and consistent balancing values to be achieved, as well as normal varus and valgus laxity angles, which may be important in obtaining optimal outcomes.

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.