Faculty Bibliography

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.

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/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

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

The geometry of the intercondylar box plays a significant role in the development of patellar clunk syndrome. We reviewed the incidence of patella clunk at mid-to-long-term follow-up of a rotating high-flex versus fixed bearing posterior stabilized TKA design. 188-mobile and 223-fixed bearing TKAs were reviewed for complications, incidence of patellar clunk, treatment, recurrence rates, range of motion, and patient satisfaction. Patellar clunk developed in 22 knees in the mobile (11.7%) and in 4 (1.8%) in the fixed bearing group (P<0.001). 23 out of 26 cases resolved with a single arthroscopic treatment and 2 resolved with a second procedure. The mean postoperative range of motion was 122.4 degrees . All but one patient reported overall satisfaction with the index procedure. In contrast with other recent studies we found a significant incidence of patellar clunk in high-flex mobile bearings. Despite the high rate of patellar clunk syndrome, overall patients did well and were satisfied with their outcomes.

BACKGROUND: In total knee surgery, typically the bone cuts are made first to produce the correct overall alignment. This is followed by balancing, often using spacer blocks to obtain equal parallel gaps in flexion and extension. Recently an electronically instrumented tibial trial has been introduced, which measures lateral and medial contact forces. The goal of our study was to determine the effect of different surgical variables; changing component sizes, modifying bone cuts, or ligament releases; on the contact forces, as a method to achieve balancing. METHODS: A special rig was designed to fit on a standard operating table, on which tests on 10 lower extremity specimens were carried out. After making bone cuts for a posterior cruciate retaining knee using a navigation system, tibial thickness was determined in extension using the Sag Test. Different Surgical Variables were then implemented, and the changes in the condylar forces were determined throughout flexion using the Heel Push Test. RESULTS: condylar forces were found to consist of gravity forces due to the weight of the leg plus forces due to pretension in the collateral ligaments. The pretension force averaged 145N but there was considerable variation because of ligament stiffness properties. Balancing from an imbalanced state could be achieved with adjustments within only 2 degrees or 2mm. CONCLUSION: The instrumented tibial trial provided force information which indicated which surgical correction options to carry out to achieve balancing. From an initial unbalanced state, relatively small changes could produce balancing, indicating the sensitivity of the procedure. CLINICAL RELEVANCE: Non-clinical. This study will assist in the balancing of the knee at total knee replacement surgery.

Knee malalignment during total knee arthroplasty (TKA) is commonly classified as either varus or valgus on the basis of a standing anteroposterior radiograph. Computer-assisted surgery (CAS) navigation TKA provides precise dynamic evaluation of knee alignment throughout the full range of motion (FROM). The goal of this study was to classify patterns of CAS-generated knee deformity curves that match specific soft tissue contracture combinations. This can then be applied as an algorithm for soft tissue balancing on the basis of the preoperative knee deformity curve. Computer navigation-generated graphs from 65 consecutive TKA procedures performed by a single surgeon were analyzed. A stress-strain curve of the coronal alignment of the knee was recorded throughout FROM before bony resection. All graphs were classified into groups according to their pattern. Cadaveric knee models were then used to test the correlation between isolated and combined ligamentous contractures and identified CAS deformity curves. An analysis of the intraoperative knee alignment graphs revealed four distinct patterns of coronal deformity on the basis of intraoperative data: 13% diagonal, 18.5% C-shaped, 43.5% comma shaped, and 25% S-shaped. Each represents the change in varus and valgus alignment during FROM. All patterns were reproduced with cadaveric knees by recreating specific contracture constellations. A tight posterior capsule gave an S-shaped curve, a tight lateral collateral ligament gave a C-shaped curve, tight medial collateral ligament gave a diagonal curve, and a tight posterior lateral corner gave a comma-shaped curve. Release of the specific contractures resulted in correction of all patterns of deformity as measured by CAS. We propose a new classification system for coronal plane knee deformity throughout FROM. This system intends to match individual and combined soft tissue pathological contractures to specific stress-strain curves obtained through routine knee CAS preparation. This classification system may provide surgeons with a general guide for soft tissue balancing during computer-navigated TKA.

Incorrect registration during computer assisted total knee arthroplasty (CA-TKA) leads to malposition of implants. Our aim was to evaluate the tolerable error in anatomic landmark registration. We incorrectly registered the femoral epicondyles, femoral and tibial centers, as well as the malleoli and documented the change in angulation or rotation. We found that the distal femoral epicondyles were the most difficult anatomic landmarks to register. The other bony landmarks were more forgiving. Identification of the distal femoral epicondyles has a high inter-observer and intra-observer variability. Our observation that there is less than 2mm of safe zone in the anterior or posterior direction during registration of the medial and lateral epicondyles may explain the inability of CA-TKA to improve upon the outcomes of conventional TKA.

Introduction: The Northern approach is a muscle sparing surgical approach to the hip that allows accurate placement of components while avoiding intraoperative dislocation. This technique minimises the known risk of DVT and leg swelling associated with dislocation, allowing for a rapid recovery when compared to the standard posterior approach. Method: To date there have been 208 consecutive total hip replacements done with Northern approach by a single surgeon. All cases were primary total hip replacements. Post operatively they were managed with standard hip precautions for 3 weeks followed by allowing increased flexion to 120 degrees and hip circumduction exercises. Average follow up was 12 months (range 1-24). Patients were followed for satisfaction, complications, postoperative rehabilitation and leg swelling. Leg swelling was monitored by measuring thigh circumference. Results: The outcomes were measured using a patient satisfaction survey with 97% having good to excellent results. There was no increase in complications rates. Intraoperative 3 (1.5%) patients needed cerclage wire around the neck due to a non-displaced intraoperative fracture. Postoperative one patient underwent revision surgery due to fracture-dislocation after falling and one patient had a single anterior dislocation. Wound complications or sepsis was not observed. Two patients had U.S confirmed DVT with one progressing to PE. The average limb lengthening was less than 3mm. The Average length of hospital stay was 3.5 days and the average recovery time was 2.6 weeks to ambulation without an assistive device. Conclusion: The Northern approach for total hip arthroplasty is safe and allows faster recovery when compared to the conventional posterior approach. The long term advantages and the possibility of decreased rates of DVT will continue to be investigated as more patients are enrolled and monitored for longer periods of time