Pain immediately following total knee arthroplasty (TKA) is often severe and can inhibit patients' rehabilitation. Recently, adductor canal blocks have been shown to provide adequate analgesia and spare quadriceps muscle strength in the early postoperative period. We devised a single injection motor sparing knee block (MSB) by targeting the adductor canal and lateral femoral cutaneous nerve with a posterior knee infiltration under ultrasound. Our primary objective was to evaluate the analgesia duration of the MSB in comparison to a standard periarticular infiltration (PAI) analgesia using patients' first rescue analgesia as the end point. Secondary outcomes measured were quadriceps muscle strength and length of stay. We randomised 82 patients scheduled for elective TKA to receive either the preoperative MSB (0.5% ropivacaine, 2.5ug/ml epinephrine, 10mg morphine, and 30mg ketorolac) or intraoperative periarticular infiltration (0.3% ropivacaine, 2.5ug/ml epinephrine, 10mg morphine, and 30mg ketorolac). Duration of analgesia, postoperative quadriceps power, and length of stay were evaluated postoperatively. Analgesic duration was found to be significantly different between groups. The MSB had a mean duration of 18.06 ± 1.68 hours while the PAI group had a mean duration of 9.25 ± 1.68 hours for a mean difference of 8.8 hours (95% CI 3.98 to 13.62), p<0.01. There were no significant differences between groups in quadriceps muscle strength power at 20 minutes (p=0.91) or 6 hours (p=0.66) after block administration. Length of stay was also not significantly different between the groups (p=0.29). Motor sparing blocks provide longer analgesia than patients receiving periarticular infiltration while not significantly reducing quadriceps muscle strength or increasing length of hospital stay

Introduction. At Sheffield Children's Hospital, treatment of leg length discrepancy is a common procedure. Historically, this has been done with external fixators. With the development in intramedullary technology, internal nails have become the preferred modality for long bone lengthening in the adolescent population. However, it is important to review whether this technology practically reduces the known challenges seen and if it brings any new issues. Therefore, the aim of this review is to retrospectively evaluate the therapeutic challenges of 16 fit-bone intramedullary femoral lengthening's at Sheffield Children's Hospital between 2021–2022. Materials & Methods. The international classification of function (ICF) framework was used to differentiate outcomes. The patient's therapy notes were retrospectively reviewed for themes around structural, activity and participation limitation. The findings were grouped for analysis and the main themes presented. Results. There were 8 males, mean age 17.4 years (range 17–18) and 8 females, mean age 15.9 years (range 14–18). 5 right and 11 left femurs were lengthened. Underlying pathology varied amongst the 16 patients. All patients went into a hinged knee brace post operatively. Structural limitations included: pain, fixed flexion deformity of the knee, loss of knee flexion, quadriceps muscle lag, muscle spasms and gluteal weakness. The primary activity limitation was reduced weight bearing with altered gait pattern. Participation limitations included reduced school attendance and involvement in activities with peers. Access to Physiotherapy from local services varied dramatically. Five of the cohort have completed treatment. Conclusions. Anecdotally, intramedullary femoral lengthening nails have perceived benefits for families compared to external fixators in the adolescent population. However, there remain musculoskeletal and psychosocial outcomes requiring therapeutic management throughout the lengthening process and beyond. Therefore, quantifying these outcomes is essential for measuring the impact on each patient for comparison. To interpret these themes, we need to evaluate the outcomes objectively, this was not done consistently in this review. Future research should look at outcome measures that are sensitive to all aspects of the ICF. With an aim of improving the therapeutic treatment provided and the overall outcome for the children treated

Aims. The aticularis genu (AG) is the least substantial and deepest muscle of the anterior compartment of the thigh and of uncertain significance. The aim of the study was to describe the anatomy of AG in cadaveric specimens, to characterize the relevance of AG in pathological distal femur specimens, and to correlate the anatomy and pathology with preoperative magnetic resonance imaging (MRI) of AG. Methods. In 24 cadaveric specimens, AG was identified, photographed, measured, and dissected including neurovascular supply. In all, 35 resected distal femur specimens were examined. AG was photographed and measured and its utility as a surgical margin examined. Preoperative MRIs of these cases were retrospectively analyzed and assessed and its utility assessed as an anterior soft tissue margin in surgery. In all cadaveric specimens, AG was identified as a substantial structure, deep and separate to vastus itermedius (VI) and separated by a clear fascial plane with a discrete neurovascular supply. Mean length of AG was 16.1 cm ( ± 1.6 cm) origin anterior aspect distal third femur and insertion into suprapatellar bursa. In 32 of 35 pathological specimens, AG was identified (mean length 12.8 cm ( ± 0.6 cm)). Where AG was used as anterior cover in pathological specimens all surgical margins were clear of disease. Of these cases, preoperative MRI identified AG in 34 of 35 cases (mean length 8.8 cm ( ± 0.4 cm)). Results. AG was best visualized with T1-weighted axial images providing sufficient cover in 25 cases confirmed by pathological findings.These results demonstrate AG as a discrete and substantial muscle of the anterior compartment of the thigh, deep to VI and useful in providing anterior soft tissue margin in distal femoral resection in bone tumours. Conclusion. Preoperative assessment of cover by AG may be useful in predicting cases where AG can be dissected, sparing the remaining quadriceps muscle, and therefore function. Cite this article: Bone Joint Open 2020;1-9:585–593

Introduction. Most of patients with unilateral hip disease shows muscle volume atrophy of pelvis and thigh in the affected side because of pain and disuse, resulting in reduced muscle weakness and limping. However, it is unclear how the muscle atrophy correlated with muscle strength in the patient with hip disorders. A previous study have demonstrated that the volume of the gluteus medius correlated with the muscle strength by volumetric measurement using 3 dimensional computed tomography (3D-CT) data, however, muscles influence each other during motions and there is no reports focusing on the relationship between some major muscles of pelvis and thigh including gluteus maximus, gluteus medius, iliopsoas and quadriceps and muscle strength in several hip and knee motions. Therefore, the purpose of the present study is to evaluate the relationship between muscle volumetric atrophy of major muscles of pelvis and thigh and muscle strength in flexion, extension and abduction of hip joints and extension of knee joint before surgery in patients with unilateral hip disease. Material and Methods. The subjects were 38 patients with unilateral hip osteoarthritis, who underwent hip joint surgery. They all underwent preoperative computed tomography (CT) for preoperative planning. There were 6 males and 32 females with average age 59.5 years old. Before surgery, isometric muscle strength in hip flexion, hip extension, hip abduction and knee extension were measured using a hand held dynamometer (µTas F-1, ANIMA Japan). Major muscles including gluteus maximus, gluteus medius, iliopsoas and quadriceps were automatically extracted from the preoperative CT using convolutional neural networks (CNN) and were corrected manually by the experienced surgeon. The muscle volumetric atrophy ratio was defined as the ratio of muscle volume of the affected side to that of the unaffected side. The muscle weakness ratio was defined as the ratio of muscle strength of the affected side to that of the unaffected side. The correlation coefficient between the muscle atrophy ratio and the muscle weakness ratio of each muscle were calculated. Results. The average muscle atrophy ratio was 84.5% (63.5%–108.2%) in gluteus maximus, 86.6% (65.5%–112.1%) in gluteus medius, 81.0% (22.1%–130.8%) in psoas major, and 91.0% (63.8%–127.0%) in quadriceps. The average muscle strength ratio was 71.5% (0%–137.5%) in hip flexion, 88.1% (18.8%–169.6%) in hip abduction, 78.6% (21.9%–130.1%) in hip extension and 84.3% (13.1%–122.8%) in knee extension. The correlation coefficient between the muscle atrophy and the ratio of each muscle strength between the affected and unaffected side were shown in Table 1. Conclusion. In conclusion, the muscle atrophy of gluteus medius muscle, psoas major muscle and quadriceps muscle significantly correlated with the muscle weakness in hip flexion. The muscle atrophy of psoas major muscle and quadriceps muscle also significantly correlated with the muscle weakness in knee extension. There were no significant correlation between the muscle atrophy and the muscle weakness in hip extension and abduction

Individuals with multi-compartment knee osteoarthritis (KOA) frequently experience challenges in activities of daily living (ADL) such as stair ambulation. The Levitation “Tri-Compartment Offloader” (TCO) knee brace was designed to reduce pain in individuals with multicompartment KOA. This brace uses novel spring technology to reduce tibiofemoral and patellofemoral forces via reduced quadriceps forces. Information on brace utility during stair ambulation is limited. This study evaluated the effect of the TCO during stair descent in patients with multicompartment KOA by assessing knee flexion moments (KFM), quadriceps activity and pain. Nine participants (6 male, age 61.4±8.1 yrs; BMI 30.4±4.0 kg/m2) were tested following informed consent. Participants had medial tibiofemoral and patellofemoral OA (Kellgren-Lawrence grades two to four) diagnosed by an orthopaedic surgeon. Joint kinetics and muscle activity were evaluated during stair descent to compare three bracing conditions: 1) without brace (OFF); 2) brace in low power (LOW); and 3) brace in high power (HIGH). The brace spring engages from 60° to 120° and 15° to 120° knee flexion in LOW and HIGH, respectively. Individual brace size and fit were adjusted by a trained researcher. Participants performed three trials of step-over-step stair descent for each bracing condition. Three-dimensional kinematics were acquired using an 8-camera motion capture system. Forty-one spherical reflective markers were attached to the skin (on each leg and pelvis segment) and 8 markers on the brace. Ground reaction forces and surface EMG from the vastus medialis (VM) and vastus lateralis (VL) were collected for the braced leg. Participants rated knee pain intensity performing the task following each bracing condition on a 10cm Visual Analog Scale ranging from “no pain” (0) to “worst imaginable pain” (100). Resultant brace and knee flexion angles and KFM were analysed during stair contact for the braced leg. The brace moment was determined using brace torque-angle curves and was subtracted from the calculated KFM. Resultant moments were normalized to bodyweight and height. Peak KFMs were calculated for the loading response (Peak1) and push-off (Peak2) phases of support. EMG signals were normalized and analysed during stair contact using wavelet analysis. Signal intensities were summed across wavelets and time to determine muscle power. Results were averaged across all 3 trials for each participant. Paired T-tests were used to determine differences between bracing conditions with a Bonferroni adjustment for multiple comparisons (α=0.025). Peak KFM was significantly lower compared to OFF with the brace worn in HIGH during the push-off phase (p Table 1: Average peak knee flexion moments, quadriceps muscle power and knee pain during stair descent in 3 brace conditions (n=9). Quadriceps activity, knee flexion moments and pain were significantly reduced with TCO brace wear during stair descent in KOA patients. These findings suggest that the TCO assists the quadriceps to reduce KFM and knee pain during stair descent. This is the first biomechanical evidence to support use of the TCO to reduce pain during an ADL that produces especially high knee forces and flexion moments. For any figures or tables, please contact the authors directly

We hypothesize that tethering adhesions of the quadriceps muscle are the major pathological structures responsible for a limited range of motion in the stiff arthritic knee. Forty-two modified quadriceps muscle releases were performed on 24 patients with advanced osteoarthritis scheduled for total knee arthroplasty. The ranges of motion were documented intraoperatively both before and immediately after the release. Passive flexion improved significantly in all patients (mean, 32.4 degrees of improvement, P < .001) following a modified quadriceps release, despite any presence of osteophytes or severe deformities. These results strongly implicate adhesions of the quadriceps muscle to the underlying femur, which prevent the distal excursion of the quadriceps tendon, as the restrictive pathology preventing deep flexion in patients with osteoarthritis

Introduction. A large number of total knee arthroplasty (TKA) patients, particularly in Japan, India and the Middle East, exhibit anatomy with substantial proximal tibial torsion. Alignment of the tibial components with the standard anterior-posterior (A-P) axis of the tibia can result in excessive external rotation of the tibial components with respect to femoral component alignment. This in turn influences patellofemoral (PF) mechanics and forces required by the extensor mechanism. The purpose of the current study was to determine if a rotating-platform (RP) TKA design with an anatomic patellar component reduced compromise to the patellar tendon, quadriceps muscles and PF mechanics when compared to a fixed-bearing (FB) design with a standard dome-shaped patellar component. Methods. A dynamic three-dimensional finite element model of the knee joint was developed and used to simulate a deep knee bend in a patient with excessive external tibial torsion (Figure 1). Detailed description of the model has been previously published [1]. The model included femur, tibia and patellar bones, TKA components, patellar ligament, quadriceps muscles, PF ligaments, and nine primary ligaments spanning the TF joint. The model was virtually implanted with two contemporary TKA designs; a FB design with domed patella, and a RP design with anatomic patella. The FB design was implanted in two different alignment conditions; alignment to the tibial A-P axis, and optimal alignment for bone coverage. Four different loading conditions (varying internal-external (I-E) torque and A-P force) were applied to the model to simulate physiological loads during a deep knee bend. Quadriceps muscle force, patellar tendon force, and PF and TF joint forces were compared between designs. Results. The RP design demonstrated consistently lower medial-lateral (M-L) force at the PF joint than the FB design, with greater differences between designs in later flexion once the patella was engaged in the sulcus groove; root-mean-square (RMS) differences in M-L force averaged 50 N less in the RP design throughout the flexion cycle, and 70 N less after 45° flexion (Figure 2). The FB design aligned for optimal bone coverage demonstrated 15% higher M-L forces than the FB design aligned with the tibial A-P axis. RMS load required by the quadriceps muscle was 60 N lower with the RP design than the FB design throughout the cycle (Figure 2). Discussion. Comparing a RP design with an anatomic patellar component and a FB design with a domed patellar component, the RP design demonstrated lower M-L PF joint and soft-tissue extensor mechanism forces. Differences were more pronounced under conditions of high I-E torque where the RP design accommodated large relative TF rotation. Differences in FB alignment resulted in substantially different PF M-L forces; when the FB component was mal-aligned with respect to the tibial A-P axis (and the line-of-action of the patellar tendon) the resulting M-L PF force was increased. The RP design reduced the demands on the extensor mechanism and loads on the PF joint and facilitated better coverage of the resected tibial bone surface

Introduction. Patients undergoing a total knee arthroplasty (TKA) are now living longer and partaking in more active lifestyles. They expect a high level of post-operative function and long term durability of their implant. Using electromyography (EMG) analysis helps further explain biomechanical findings by giving insight as to what is occurring at the level of the muscles. Normal biomechanics are not restored post-TKA as patients have reduced knee flexion and weakened quadriceps muscles compared to their healthy peers. Purpose. The purpose of this study was to compare muscle activation in TKA patients who received a medial pivot (MP) or posterior stabilized (PS) implant to those of healthy controls (CTRL) during a stair ascent task. Methods. A total of 12 patients were assigned to either a MP or PS TKA operated by the same surgeon. Approximately 9 months following surgery, the 12 patients along with 6 CTRL patients completed an EMG analysis during a stair ascent task (Table 1). Wireless EMG electrodes were placed on 4 muscles: vastus medialis (VM), vastus lateralis (VL), biceps femoris long head (BF), and semimembranosus (SM) muscles. All participants completed maximal voluntary contractions (MVICs) during knee flexion and extension while seated with the knee flexed at 60°. Following the MVICs, participants completed 5 trials of a 3-step stair ascent task. TKA patients were instructed to make the first step onto the staircase with their operated limb. EMG data were processed in Matlab. Peak muscle activity (PeakLE EMG) and total muscle activity (iEMG) from each muscle was obtained during stance phase. Data were averaged between left and right limbs for the CTRL group and compared to the operated limb of TKA groups. Non-parametric Kruskal Wallace ANOVA tests were used to test for statistical significance between groups and Wilcoxon rank sum tests were used to identify differences with α=0.05. Results. Both TKA groups had significantly greater PeakLE EMG of the quadriceps muscles compared to the CTRL group (Figure 1). PeakLE EMG of the BF and VM muscles were significantly greater in the PS group compared to both CTRL and MP groups. The PS group had significantly greater iEMG of the BF, VL and VM muscles compared to the CTRL group (Figure 2) whereas the PS group had significantly greater iEMG of the SM and VM muscles compared to the MP group. Conclusion. The MP group had lower PeakLE EMG for both VM and BF muscles compared to the PS group, indicating that the MP group activates these muscles less to achieve the stair ascent task. BF muscle stabilizes the knee roll-back motion while the VM muscle extends the leg to clear the steps. iEMG for the VM and BF muscles were greater for the PS group indicating that they have to activate their muscles longer and to a greater extent in order to stabilize the joint. This increased stability in MP implants is achieved through the concave aspect on the medial tibial plateau for the femoral condyle to pivot in. This will reduce implant wear, prolonging implant longevity

Introduction. The purpose of this study was to determine whether the patient's perceived outcome and speed of recovery differs between a posterior cruciate ligament (PCL) substituting (cam-post type) and PCL sacrificing (ultracongruent polyethylene) total knee arthroplasty (TKA). Methods. Thirty eight patients (mean age, 65 years) underwent bilateral TKA using a PCL substituting and a PCL sacrificing prosthesis on each side. At each follow-up, the stability of anteroposterior and mediolateral laxity using stress radiographs, range of motion, quadriceps muscle power recovery using isokinetic dynamometer and radiographs were evaluated. At the 1-year evaluation, we asked, “Which is your better knee overall?” to determine the patients' preferences. Results. The mean varus/valgus laxities were 1.6Ë�/3.9Ë� in the PCL sacrificing side and 2.3Ë�/5.9Ë� in the PCL substituting side, and the mean anterior/posterior laxities were 6.4 mm/14.2 mm and 3.0 mm/7.3 mm at the 1-year follow up, respectively. Isokinetic peak torque at 60°/sec and 180°/sec in extension was 130% and 113% compared to the preoperative value in the PCL sacrificing side and 109% and 110% in the PCL substituting side, respectively. The differences in the posterior laxity and isokinetic peak torque at 60°/sec were significant statistically. Sixty-one percent preferred PCL sacrificing side to PCL substituting side. Conclusion. PCL sacrificing TKA showed more posterior laxity and better quadriceps muscle power at the time of short-term follow-up. Patients with bilateral TKA preferred PCL sacrificing TKA to PCL substituting TKA. Longer follow-up is needed to determine whether there will be an advantage in terms of longer-term function

Background. Revision total knee arthroplasties (rTKA) are performed with increasing frequency due to the increasing numbers of primary arthroplasties, but very little is known regarding the influence of muscle strength impairments on functional limitations in this population. Objectives. The aim of this study was to assess relationship between muscle strength and functional level in patient with rTKA. Design and Methods. Twenty-three patients (8 males, 15 females) were included in the study with mean age 68.4±10 years. Patients performed 3 performance tests (50-Step Walking Test, 10 Meter Walk Test, 30-Second Chair-Stand Test), and one self-report test (HSS) were preferred to assess patients. The maximum isometric muscle strength of quadriceps femoris and hamstring muscles of all the patients was measured using Hand-Held Dynamometer (HHD). Results. While moderate-to-strong significant correlations was found between quadriceps femoris muscle strength and 30- Second Chair-Stand Test (r=0.390, p=0.049), 50-Step Walking Test (r=−0.530, p=0.005), 10 Meter Walk Test (r=−0.587, p=0.002), there were not significant correlation between HSS knee score and all performance-based tests (p>0.05). Also there were not significant correlation between hamstring muscle strength and all other measurement tests (p>0.05). Conclusion. The moderate-to-strong statistical significant correlation between quadriceps femoris muscle strength and functional performance tests suggests that improved postoperative quadriceps strengthening could be important to enhance the potential benefits of rTKA

The medial patellofemoral ligament (MPFL) has been recognised as the most important medial structure preventing lateral dislocation or subluxation of the patella (LeGrand 2007). After MPFL rupture the patella deviates from the optimal path resulting in an altered retropatellar pressure distribution. This may lead to an early degeneration with loss of function and need for endoprosthetic joint replacement. The goal of this study was to develop a dynamic knee-simulator to test the influence of ligament instabilities to patella-tracking under simulation of physiological quadriceps muscle loading. On 10 fresh-frozen cadaveric knees the quadriceps muscle was divided into five parts along their anatomic fibre orientation analogous to Farahmand 1998. The muscular loading was achieved by applying weights to each of the fife components in proportion to the cross sectional muscle area. A total of 175 N was connected to the muscles using modified industrial cable connecting systems [Lancier Calbe, Drensteinfurt/Germany]. A novel light digital patellar reference base (DRB) was developed and attached to the patella with four bone screws. On addition a femoral and tibial digital reference base was constructed and secured to these two bones. Position data of the patella, the femur and tibia was tracked by a conventional tracking system [Optotrak, NDI Europe]. The relative movement between femur and tibia (“flexion path”) and patella and femur (“patella tracking”) was recorded. For retropatellar pressure measurement a custom made sensor was introduced between the patella and femur [Pliance, Novel/Germany]. The sensor consists of 85 single pressure measuring cells. The robot-control-unit is liked to a force-torque sensor (hybrid method). The force free knee-flexion-path from 0° to 90° was calculated during three “passive path” measurements using this hybrid robotic method. The actual measurements followed with identical parameters. The 3D-patella position was recorded (six degrees of freedom) along with the corresponding retropatellar pressure distribution according to knee-flexion and medial forces (intact vs. cut MPFL). Measurements were performed for the intact knee (“native”), with muscular quadriceps loading, after opening the joint capsule and with introduced pressure sensor to differentiate each of their influences. The load free knee-flexion-path (“passive path”) could be calculated for all of the ten knees and was utilised as the basis for all dynamic measurements. There was no alteration of the “flexion-path”. Thus the measurements were only influenced by the variables “capsular joint opening,” “muscular quadriceps loading” and “MPFL-tension”. The custom made connections between the five quadriceps components and weights proved to be a secure way to prevent rupture due to the applied forces of up to 70 N during the average measuring time of 7.5 h/knee. Only on one knee the Vastus lateralis obliquus muscle ruptured proximally. All reference bases were 100% visible despite the knee flexion form 0°–90°. No loosening of the reference base screws occurred. Overall the combination of a robotic-assisted, force free dynamic knee-flexion under quadriceps simulation and 3D-patella-tracking seems to be a promising method to evaluate the biomechanical influences of ligaments on the human knee

Experimental knee simulators for component evaluation or in vitro testing provide valuable insight into the mechanics of the implanted joint. The Kansas knee simulator (KKS) is an electro-hydraulic whole joint knee simulator, with five actuators at the hip, ankle and quadriceps muscle used to simulate a variety of dynamic activities in cadaveric specimens. However, the number and type of experimental tests which can feasibly be performed is limited by the need to make physical component parts, obtain cadaveric specimens and the substantial time required to carry out each test. Computational simulations provide a complementary toolset to experimental testing; experimental data can be used to validate the computational model which can subsequently be used for early evaluation and ranking of component designs. The objective of this study was to explore potential improvements to loading and boundary conditions in current computational/experimental models, specifically the KKS, in order to develop representations of several activities of daily living (ADLs) which reproduce in vivo knee joint loading measurements. An existing finite element model of the KKS was modified to extend the capability, and improve the fidelity, of the computational model beyond the experimental setup. An actuator to allow anterior-posterior (A-P) motion of the hip was included and used to prescribe relative hip-ankle A-P kinematics during the simulations. The quadriceps muscle, which in the experimental simulator consisted of a single quadriceps bundle with a point-to-point line of action, was divided into four heads of the quadriceps with physiological muscle paths. The hamstrings muscle, which was not present in the experiment, was represented by point-to-point actuators in four bundles. A flexible control system was developed which allowed control of the quadriceps and hamstrings actuators to match a knee flexion profile, similar to actuation of the experimental KKS, but also allowed control of the compressive tibiofemoral (TF) joint force, medial-lateral (M-L) load distribution, internal-external (I-E) torque and A-P load at the joint. A series of sensors, measuring all six load components on the medial and lateral compartments of the tibial insert, as well as knee flexion angle, were incorporated into the simulation. Instantaneous measurements from the sensors were fed to a control system, implemented within an Abaqus/Explicit user subroutine (Figure 1). The controller was used to drive actuators in the FE model to match target in vivo joint loading profiles, measured from telemetric patient data. The control system was applied to recreate in vivo loading conditions at the knee joint during three ADLs for three different subjects (Figure 2), with excellent agreement between simulation joint loading conditions and the target profiles; RMS differences were less than 1°, 80N, 2.5%, and 0.8Nm for knee flexion angle, compressive joint load, M-L load split and I-E torque, respectively, throughout the cycle for all three activities (Figure 3). The flexible nature of the control system ensures that it can be used to evaluate an expansive variety of ‘effect of’ studies, as well as to determine advanced loading profiles for the experimental simulator

INTRODUCTION. The medial patellofemoral ligament (MPFL) has been recognised as the most important medial structure preventing lateral dislocation or subluxation of the patella (LeGrand 2007). After MPFL rupture the patella deviates from the optimal path resulting in an altered retropatellar pressure distribution. This may lead to an early degeneration with loss of function and need for endoprosthetic joint replacement. The goal of this study was to obtain first data about retropatellar pressure distribution under simulation of physiological quadriceps muscle loading and evaluate the influence of ligament instabilities. MATERIALS AND METHOD. On ten fresh-frozen cadaveric knees the quadriceps muscle was divided into 5 parts along their anatomic fiber orientation analogous to Farahmand 1998. Muscular loading was achieved by applying weights to each of the five components in proportion to the cross sectional muscle area (total load 175 N). A custom made sensor was introduced between the patella and femur [Pliance, Novel / Germany]. The sensor consists of 85 single cells. The robot-control-unit is liked to a force-torque sensor. The force free knee-flexion-path from 0° to 90° was calculated during three “passive path” measurements. The actual measurements followed with identical parameters. At first, the retropatellar pressure distribution was recorded with intact ligaments (“native”). After cutting the MPFL the test was repeated. Then double bundle MPFL reconstruction (Schoettle 2009) was performed and the pressure distribution was obtained again. Minimum, mean and maximum pressures and forces were statistically compared in each of the three tested conditions (native Patella with intact MPFL, cut and reconstructed MPFL). We followed the hypothesis that MPFL reconstruction can restore native retropatellar pressure distribution. RESULTS. Mean retropatellar force measured in all conditions of the MPFL was 64.29 N [F. min. 0.06, F. max. 194.91, SD 66.99] N. Mean retropatellar pressure was 285.69 [P. min. 0.00, P. max. 923.64, SD 303.73] kPa. The mean retropatellar force increased with knee flexion from 35 N [0° flexion] to 75 N [90° flexion]. After cutting the MPFL mean force decreased in all degrees of flexion compared to the native state but mean pressure increased for the first 50° of flexion. Reconstruction of the MPFL did not restore native conditions. The mean pressure was only 3 N above the one of the cut MPFL. Regarding the entire retropatellar surface, maximum pressure decreased with increasing degrees of flexion from 330 kPa to 275 KPa. After cutting the MPFL, maximum pressure decreased about 60 kPa. MPFL reconstruction resulted in an increased maximum pressure (+ 10 kPa) in all degrees of flexion, but the values of the native state could not be achieved. To our knowledge this is the first experimental data of dynamic retropatellar pressure measurements on human cadaver knees in which a force free knee flexion is performed by an industrial robot under muscular quadriceps loading. There were no significant changes in retropatellar pressures after cutting the MPFL. In contrast to our hypothesis, MPFL reconstruction does not restore native conditions at this experimental setting

Background. In vivo fluoroscopic studies have proven that femoral head sliding and separation from within the acetabular cup during gait frequently occur for subjects implanted with a total hip arthroplasty. It is hypothesized that these atypical kinematic patterns are due to component malalignments that yield uncharacteristically higher forces on the hip joint that are not present in the native hip. This in vivo joint instability can lead to edge loading, increased stresses, and premature wear on the acetabular component. Objective. The objective of this study was to use forward solution mathematical modeling to theoretically analyze the causes and effects of hip joint instability and edge loading during both swing and stance phase of gait. Methods. The model used for this study simulates the quadriceps muscles, hamstring muscles, gluteus muscles, iliopsoas group, tensor fasciae latae, and an adductor muscle group. Other soft tissues include the patellar ligament and the ischiofemoral, iliofemoral, and pubofemoral hip capsular ligaments. The model was previously validated using telemetric implants and fluoroscopic results from existing implant designs. The model was used to simulate theoretical surgeries where various surgical alignments were implemented and to determine the hip joint stability. Parameters of interest in this study are joint instability and femoral head sliding within the acetabular cup, along with contact area, contact forces, contact stresses, and ligament tension. Results. During swing phase, it was determined that femoral head pistoning is caused by hip capsule laxity resulting from improperly positioned components and reduced joint tension. At the point of maximum velocity of the foot (approximately halfway through), the momentum of the lower leg becomes too great for a lax capsule to properly constrain the hip, leading to the femoral component pistoning outwards. This pistoning motion, leading to separation, is coupled with a decrease in contact area and an impulse-like spike in contact stress (Figure 1). During stance phase, it was determined that femoral head sliding within the acetabular cup is caused by the proprioceptive notion that the human hip wants to rotate about its native, anatomical center. Thus, component shifting yields abnormal forces and torques on the joint, leading to the femoral component sliding within the cup. This phenomenon of sliding yields acetabular edge-loading on the supero-lateral aspect of the cup (Figure 2). It is also clear that joint sliding yields a decreased contact area, in this case over half of the stable contact area, corresponding to a predicted increase in contact stress, in this case over double (Figure 2). Discussion. From our current analysis, the causes and effects of hip joint instability are clearly demonstrated. The increased stress that accompanies the pistoning/impulse loading scenarios during swing phase and the supero-lateral edge-loading scenarios during stance phase provide clear explanations for premature component wear on the cup, and thus the importance of proper alignment of the THA components is essential for a maximum THA lifetime. For any figures or tables, please contact authors directly

“The shortest distance between two points is a straight line.” This explains many cases of patellar maltracking, when the patellar track is visualised in three dimensions. The three-dimensional view means that rotation of the tibia and femur during flexion and extension, as well as rotational positioning of the tibial and femoral components are extremely important. As the extensor is loaded, the patella tends to “center” itself between the patellar tendon and the quadriceps muscle. The patella is most likely to track in the trochlear groove IF THE GROOVE is situated where the patella is driven by the extensor mechanism: along the shortest track from origin to insertion. Attempts to constrain the patella in the trochlear groove, if it lies outside that track, are usually unsuccessful. Physiologic mechanisms for tibial-femoral rotation that benefit patellar tracking (“screw home” and “asymmetric femoral roll-back”) are not generally reproduced. Practical Point. A patellofemoral radiograph that shows the tibial tubercle, illustrates how the tubercle, and with it the patellar tendon and patella itself, are all in line with the femoral trochlea. To accomplish this with a TKA, the femoral component is best rotated to the transepicondylar axis (TEA) and the tibial component to the tubercle. In this way, when the femoral component sits in its designated location on the tibial polyethylene, the trochlear groove will be ideally situated to “receive” the patella. Knee Mechanics. Six “degrees of freedom” refers to translation and rotation on three axes (x,y,z). This also describes how arthroplasty components can be positioned at surgery. The significant positions of tibial, femoral and patellar components are: 1. Internal-external rotation (around y-axis) and 2. Varus-valgus rotation (around z axis). 3. Medial-lateral translation (on x-axis). The other positional variables are less important for patella tracking. Biomechanical analyses of knee function are often broken down into: i. Extensor power analysis (y-z or sagittal plane) and ii. Tracking (x-y or frontal plane). These must be integrated to include the effects of rotation and to better understand patellar tracking. Effect of Valgus. Frontal plane alignment is important but less likely to reach pathological significance for patellar tracking than rotational malposition clinically. For example if a typical tibia is cut in 5 degrees of unintended mechanical valgus, this will displace the foot about 5 cm laterally but the tibial tubercle only 8 mm laterally. An excessively valgus tibial cut will not displace the tubercle and the patella as far as mal-rotation of the tibial component. Effect of Internal Rotation of Tibial Component. By contrast, internal rotation of the tibial component by 22 degrees, which is only 4 degrees in excess of what has been described as tolerable by Berger and Rubash, displaces the tubercle 14 mm, a distance that would place the center of most patella over the center of the lateral femoral condyle, risking dislocation. Dynamically, as the knee flexes, if the tibia is able to rotate externally this forces the tubercle into an even more lateral position, guaranteeing that the patella will align lateral to the tip of the lateral femoral condyle, and dislocate. The design of femoral components, in particular the varus-valgus angle of the trochlear groove, has an effect on patellar tracking. This effect will be accentuated by the surgical alignment technique of the femoral and tibial components. Component positions that mimic the orientation of the normal anatomy usually include more valgus alignment of the femoral component. This rotates the proximal “entrance” of the femoral trochlear groove more medially, making it more difficult for the patella to descend in the trochlear groove

Background. Currently, hip implant designs are evaluated experimentally using mechanical simulators or cadavers, and total hip arthroplasty (THA) postoperative outcomes are evaluated clinically using long-term follow-up. However, these evaluation techniques can be both costly and time-consuming. Fortunately, forward solution mathematical models can function as theoretical joint simulators, providing instant feedback to designers and surgeons alike. Recently, a validated forward solution model of the hip has been developed that can theoretically simulate new implant designs and surgical technique modifications under in vivo conditions. Objective. The objective of this study was to expand the use of this hip model to function as an intraoperative virtual implant tool, thereby allowing surgeons to predict, compare, and optimize postoperative THA outcomes based on component placement, sizing choices, reaming and cutting locations, and surgical methods. Methods. The math model simulates the quadriceps muscles, hamstring muscles, gluteus muscles, iliopsoas muscles, tensor fasciae latae, and an adductor muscle group, as well as the ischiofemoral, iliofemoral, and pubofemoral hip capsular ligaments. The model can simulate resecting, weakening, loosening, or tightening of soft tissues based on surgical techniques. Additionally, the model can analyze a variety of activities, both weight-bearing and non-, including swing and stance phase of gait, deep knee bend, and more. The model was previously validated using telemetric implants and fluoroscopic results from existing implant designs. Results. First, the model tool has capabilities that will allow surgeons to pre- or intra-operatively experiment with various surgical alignments, component designs, sizes, and offsets, as well as reaming and cutting locations. The model tool will incorporate a built-in CT scan bone database which will assist in determining muscle and ligament attachment sites as well as bony landmarks. The model tool can be used to assist in the placement of both the femoral component (Figure 1) and the acetabular cup (Figure 2). Moreover, once the surgeon has decided on the placements of the components, he or she can use the modelling capabilities of the tool to run virtual simulations based on the chosen parameters. The simulations will reveal force and motion predictions of the hip joint based on the current component positioning (Figure 3). The surgeon can then choose to modify the positions accordingly or proceed with the surgery. Discussion. Being able to intraoperatively predict postoperative mechanics will improve the functional outcomes of total hip arthroplasty and reduce the frequency of postoperative complications

Osteoarthritis (OA) is a highly prevalent disease that has a debilitating role in every day function and activity. In 2002, the indirect cost of OA was 5 billion dollars, secondary to absenteeism and loss of productivity. There are multiple management options available for OA, with surgery usually being a last resort. Total knee arthroplasty (TKA) provides a long-lasting treatment option with excellent results. However, a high proportion of patients still express dissatisfaction following surgery, possibly due to a combination of pain, continued limitation of function, and high expectations. The use of bracing provides a non-operative treatment option as well as a useful therapy adjunct in patients who undergo TKA. Bracing may aid in rehabilitation prior to TKA as well as postoperatively, and it also plays a beneficial role in problematic situations, such as patients who have undergone revision surgery or who have extensor mechanism problems. They are thought to aid in gait ‘retraining’, quadriceps muscle strengthening, improving joint alignment, and increasing stability of the joint. Although the American Academy of Orthopedic Surgeons remains inconclusive on the role of bracing, multiple studies have highlighted that they may be of benefit. The use of valgus bracing has been shown to provide short-term treatment for activity, bracing for uni-compartmental OA has shown an improvement in outcome measures, and the use of an unloader brace has led to improved general physical health and function outcomes, as measured by the SF-12 and WOMAC, respectively

Background. While not common in the native hip, occurrences of femoral head separation from the acetabular cup during gait are well documented after total hip arthroplasty. Although the effects of this phenomenon are not well understood, we hypothesize that these atypical kinematics are due to component misalignments that yield uncharacteristic forces on the hip joint that are not present in the native hip. Objective. The objective of this study was to theoretically predict the causes of hip separation during stance phase using forward solution mathematical modelling. Methods. The model simulates the quadriceps muscles, hamstring muscles, gluteus muscles, iliopsoas group, tensor fasciae latae, and an adductor muscle group. Other soft tissues include the patellar ligament and the ischiofemoral, iliofemoral, and pubofemoral hip capsular ligaments. The model was previously validated using telemetric implants and fluoroscopic results from existing implant designs. The model is currently being used to analyze the effects that various surgical alignments have on hip separation. Specifically, this study analyzed 4 different hypothetical patients under the same 87 alignment conditions during stance phase. Alignment conditions include anatomical component alignment, intended acetabular cup medial and superior shifts, unintended cup medial and superior reaming errors, variations in cup version angles, leg length discrepancies, and femoral component offset modifications. Results. During stance phase, it was determined that acetabular cup placement had a much more substantial effect on hip separation than femoral component placement. While neither femoral offset nor leg length discrepancy showed a correlation to hip separation, both medial and superior shifting of the acetabular cup showed a positive trend with increased hip separation. Figure 1 shows a comparison of average hip separation with intended shifts in the cup (0mm, 2mm, or 5mm) plus unintended reaming errors (0mm to 10mm extra) Furthermore, larger intended shifts in cup placement yielded smaller margins of error (Figure 2). Observe in Figure 2 how an increase in the size of the blue region (intended shifting region) correlates to a decrease in size of the green region (allowable error region where hip separation will not occur). It was also determined that cup version angles have less of a defined effect on hip separation, as the relationship between angular position and hip separation varied between patients. Discussion. From our current analysis, the importance of proper alignment of the acetabular cup can be clearly seen. Overall, it has been shown that reaming errors of as low as 2 mm can yield separation magnitudes up to 2 mm (and potentially greater)

Introduction. The legacy constrained condylar knee prosthesis (LCCK, Zimmer.) is designed for primary and revision total joint arthroplasties that need additional stability due to ligament deficiency and to compensate for bone defects. In this follow-up we present our mid term results. Methods and Material. Between November 1999 and January 2006 59 patients were provided with 67 LCCK knee endoprotheses. 38 prostheses were implanted in cases of revision surgery and 29 as primary implants. The mean patient age was 76 years (range 22–93). Indications for revisions were 20 aseptic loosenings, 11 late infections, 7 instabilities (5 cases due to polyethylene wear). Indications for primary arthroplasties were 16 severe valgus and 7 severe varus deformities, 5 cases of osteoarthritis after infection and 1 posttraumatic deformity. 36 femur components (54%) and 34 tibia components (51%) were augmented. 31 stems were fixed cementless, 15 stems were cemented (6 with an intermedullary plug). We evaluated the results prospectively with a clinical inspection and x-ray. Clinical rating systems used were the Knee society, SF-36 Quality of life and Womac score. The mean follow up was 5.6 years. 42 patients were examined, 10 questioned on the telephone, 3 deceased, 12 had to be revised and 2 were lost for follow-up. Results. We had an increase in ROM from 93° to 110°. The Knee Society score improved from 40 to 75 and the function score improved from 46 to 72. The early complications included 1 peroneal lesion, 1 intraoperative fracture, 7 limitations in movement, 10 wound healing problems and 1 thrombosis. 12 revisions had to be performed. 1 septic loosening, 1 synovectomy, 4 aseptic loosenings, 3 secondary patella replacements, 1 traumatic rupture of the quadriceps muscle, 1 chondrosacroma and 1 revision performed in another clinic. 25 (80%) uncemented stems, 3 (33%) cemented stems and 1 (17%) of the stems cemented with an intramedullary plug showed radiolucencies. Conclusion. The LCCK prosthesis can be recommended as a primary implant and for revisions in cases of severe instability or severe bone loss. Due to the bad general health of the patients and preoperative situation of the knee joints the results are satisfactory. All revisions due to aseptic loosening had to be performed on LCCKs with uncemented stems

Background. Data on varus-valgus and rotational profiles can be obtained during navigated total knee arthroplasty (TKA). Such intraoperative kinematic data might provide instructive clinical information for refinement of surgical techniques, as well as information on the anticipated postoperative clinical outcomes. However, few studies have compared intraoperative kinematics and pre- and postoperative clinical outcomes; therefore, the clinical implications of intraoperative kinematics remain unclear. In clinical practice, subjects with better femorotibial rotation in the flexed position often achieve favorable postoperative range of motion (ROM); however, no objective data have been reported to prove this clinical impression. Hence, the present study aimed to investigate the correlation between intraoperative rotation and pre- and postoperative flexion angles. Materials and Methods. Twenty-six patients with varus osteoarthritis undergoing navigated posterior-stabilized TKA (Triathlon, Stryker, Mahwah, NJ) were enrolled in this study. An image-free navigation system (Stryker 4.0 image-free computer navigation system; Stryker) was used for the operation. Registration was performed after minimum soft tissue release and osteophyte removal. Then, maximum internal and external rotational stress was manually applied on the knee with maximum extension and 90° flexion by the same surgeon, and the rotational angles were recorded using the navigation system. After knee implantation, the same rotational stress was applied and the rotational angles were recorded again. In addition, ROM was measured before surgery and at 1 month after surgery. The correlation between the amount of pre- and postoperative tibial rotation and ROM was statistically evaluated. Results. The amount of tibial rotation at registration was positively correlated with that after surgery (p < 0.05). Although the amount of tibial rotation at maximum extension was not correlated with ROM, the amount of rotation at 90° flexion at registration was positively correlated with pre- and postoperative ROM (p < 0.05). Moreover, the amount of tibial rotation at 90° flexion was positively correlated with postoperative ROM (p < 0.05). Conclusion. It is well known that preoperative ROM affects postoperative ROM. Our results showed that better tibial rotation at 90° flexion predicts favorable postoperative ROM, suggesting that flexibility of the surrounding soft tissues as well as the quadriceps muscles is an important factor for obtaining better ROM. Further evaluation of navigation-based kinematics during TKA surgery may provide useful information on ROM