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

Many patients who undergo a total knee arthroplasty (TKA) wish to return to a more active lifestyle. The implant must be able to restore adequate muscle strength and function. However, this may not be a reality for some patients as quadriceps and hamstrings muscle activity may remain impaired following surgery. The purpose of this study was to compare muscle activity between patients implanted with a medial pivot (MP) or posterior stabilized (PS) implant and controls (CTRL) during ramp walking tasks. Fifteen patients were assigned to either a MP (n=9) or PS (n=6) TKA operated by the same surgeon. Nine months following surgery, the 15 patients along with nine CTRL patients completed motion and EMG analysis during level, ramp ascent & descent walking tasks. Wireless EMG electrodes were placed on six muscles: vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF), semimembranosus (SM) muscles, gastrocnemius medial head (GM), and gastrocnemius lateral head (GL). Participants completed three trials of each condition. EMG data were processed for an entire gait cycle of the operated limb in the TKA groups, and for the dominant limb in the CTRL group. The maximum muscle activity achieved with each muscle during the level trial was used to normalize the ramp trials. The onset and offset of each muscle was determined using the approximated generalized likelihood ratio. Peak muscle activity (PeakLE), total muscle activity (iEMG), and muscle onsets/offsets were determined for each muscle for the ramp ascent and descent trials. Non-parametric Kruskal Wallace tests were used to test for statistical significance between groups with α=0.05. During the ramp up task, both MP and PS groups had significantly greater PeakLE and iEMG for the hamstring muscles compared to the CTRL, whereas the PS group had significantly greater PeakLE compared with the MP group for the SM muscle. During the ramp down task, both MP and PS groups had significantly greater PeakLE and iEMG for the SM and GL muscles compared to the CTRL. The PS group also had significantly greater iEMG for the BF and VM muscles compared to the CTRL. The MP group had a significantly earlier offset for the SM muscle compared to the CTRL. Stability in a cruciate removing TKA is partially controlled by the prosthetic design. During the ramp up task, the TKA groups compensated the tibial anterior translation by activating their hamstrings more and for a longer duration. The MP group required less hamstrings activation than the PS group. During the ramp down task, TKA patients stiffened their knee in order to stabilize the joint. The quadriceps, hamstrings and GL muscle were activated more and for a longer duration than the CTRL group to protect the tibial posterior translation. The PS group required greater BF and VM iEMG than the MP group. Even if surgery reduced pain, differences in muscle activity exist between TKA patients and healthy controls. The prosthetic design provides some stability to the knee, and the MP implant required less muscle activation than the PS implant to stabilize the knee joint

Introduction. Unicompartmental knee arthroplasty (UKA) currently experiences increased popularity. It is usually assumed that UKA shows kinematic features closer to the natural knee than total knee arthroplasty (TKA). Especially in younger patients more natural knee function and faster recovery have helped to increase the popularity of UKA. Another leading reason for the popularity of UKA is the ability to preserve the remaining healthy tissues in the knee, which is not always possible in TKA. Many biomechanical questions remain, however, with respect to this type of replacement. 25% of knees with medial compartment osteoarthritis also have a deficient anterior cruciate ligament [1]. In current clinical practice, medial UKA would be contraindicated in these patients. Our hypothesis is that kinematics after UKA in combination with ACL reconstruction should allow to restore joint function close to the native knee joint. This is clinically relevant, because functional benefits for medial UKA should especially be attractive to the young and active patient. Materials and Methods. Six fresh frozen full leg cadaver specimens were prepared to be mounted in a kinematic rig (Figure 1) with six degrees of freedom for the knee joint. Three motion patterns were applied: passive flexion-extension, open chain extension, and squatting. These motion patterns were performed in four situations for each specimen: with the native knee; after implantation of a medial UKA (Figure 2); next after cutting the ACL and finally after reconstruction of the ACL. During the loaded motions, quadriceps and hamstrings muscle forces were applied. Infrared cameras continuously recorded the trajectories of marker frames rigidly attached to femur, tibia and patella. Prior computer tomography allowed identification of coordinate frames of the bones and calculations of anatomical rotations and translations. Strains in the collateral ligaments were calculated from insertion site distances. Results. Knee kinematics and collateral ligament strains were quite close to the native situation after both UKA and ACL reconstruction for all motor tasks. Nevertheless, some statistically significant differences were detected, which may be relevant clinically and biomechanically. In general, insertion of a UKA led to a knee joint which was somewhat less adducted (Figure 3), with a medial femoral condyle located slightly higher, confirming previously published findings [2]. These effects were slightly reduced both after cutting as well as after reconstructing the ACL. The joint became somewhat less stable in the AP direction after insertion of a UKA and this instability persisted not only after cutting but even after reconstructing the ACL

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

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

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)

The purpose of this study was to compare lower limb muscle activity in patients who underwent a total knee arthroplasty (TKA) with a medial pivot (MP) implant to healthy controls (CTRL) during a stair ascent task. Seven MP (age: 61.4±6.5 years, BMI: 30.0±4.7 kg/m2, 12.4±3.8 months post-surgery) patients who underwent a TKA performed using either a subvastus or medial parapatellar approach were age- and BMI-matched to seven healthy CTRL participants (age: 62.4±4.2 years, BMI: 26.3±2.7 kg/m2) for comparison in this study. Participants underwent electromyography (EMG) analysis while completing a three-step stairs ascent task. Portable wireless surface EMG probes were placed on the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF) and semimembranous (SM) muscles of both lower limbs. Peak linear envelope (peakLE) and total muscle activity (iEMG) were extrapolated and normalised to a maximal voluntary contraction. Nonparametric Kruskal Wallace ANOVA tests were used and Wilcoxon rank sum tests were used to identify where significant (p < 0.05) differences occurred. The operated limb had significantly lower iEMG in the VAL, RF and BF muscles, and significantly lower peakLE in the SM muscle compared to the non-operated limb. The operated-limb of the MP group had significantly lower iEMG in the VAL and BF muscles, and significantly lower peakLE in the VAL, RF and SM muscles compared to the CTRL group. The non-operated limb in the MP group had significantly larger peakLE and iEMG in the RF muscle compared to the CTRL group. Differences in muscle activity between the operated and non-operated limbs in TKA patients with a MP implant demonstrates a compensatory strategy to reduce loading on the operated limb by relying on the non-operated limb. This same strategy has been reported in other studies investigating other functional tasks. This reliance on the non-operated limb resulted by having greater peakLE and iEMG in the RF muscle compared to the healthy CTRLs. These differences between limbs could also result from many years of muscle adaptation waiting to receive a knee replacement. In conclusion, TKA patients exhibit discrepancies in muscle activity compared to healthy knees and differences between operated and non-operated limbs. Post-surgery rehabilitation should rely on unilateral strength exercises of the quadriceps and hamstrings muscles to reduce discrepancies to allow for a more balanced muscle activity between limbs

Introduction. Total knee arthroplasty (TKA) is a well proven surgical procedure. Squat and gait motions are common activities in daily life. However, squat motion is known as most dissatisfying motion in activities in daily life after total knee arthroplasty (TKA). Dissatisfaction after TKA might refer to muscle co-contraction between quadriceps and hamstrings. The purposed of this study was to develop squat and gait simulation model and analyses the contact mechanics and quadriceps and hamstring muscle stability. We hypothesized that squat model shows larger contact forces and lower hamstring to quadriceps force ratio than gait model. Materials and Methods. Squat motion and gait model were simulated in musculoskeletal simulation software (AnyBody Modeling System, AnyBody Technology, Denmark). Subject-specific bone models used in the simulation were reconstructed from CT images by Mimics (Materialize, Belgium). The lower extremity model was constructed with pelvis, femur, tibia, foot segments and total knee replacement components: femoral component, tibial insert, tibial tray, and patella component [Fig.1]. The muscle model was consisted of 160 muscle elements. The TKR components used in this study are PS-type LOSPA Primary Knee System (Corentec Co., Ltd, Republic of Korea). Force-dependent kinematics method was used in the simulation. The model was simulated to squat from 15° to 100° knee flexion, in 100 frames. Gait simulation model was based on motion capture and force-plate system. Motion capture and force-plate data were from grand challenge competition dataset. Results / Discussion. Patellofemoral contact forces ranged from 0.18 to 3.78 percent body weight (%BW) and from 0.00 to 1.36 %BW during squat motion and gait cycle, respectively. Patellofemoral contact forces calculated at 30°, 60°, and 90° flexion during squat motion were 0.53, 1.93, and 3.22 %BW, respectively. Wallace et al. also reported patellofemoral contact forces at 30°, 60°, and 90° flexion, which were 0.31, 1.33, 2.45 %BW during squat motion. Our results showed similar results from other studies, however the squat model overestimated the patellofemoral contact forces. Contact stiffness in the simulation model might affected the overestimated contact forces. Hamstring to quadriceps force ratio ranged from 0.32 to 1.88 for squat model, and from 0.00 to 2.54 for gait model. As our hypothesis, squat motion showed larger patellofemoral contact forces. Also, mean hamstring to quadriceps force ratio of squat model were about half than the mean hamstring to quadriceps force ratio of gait model. From the results, possibility exists that unbalanced force of quadriceps and hamstring can affect dissatisfaction after TKA while squat motion is the most dissatisfying motion after TKA. However, muscle stability is not the only factor that can affect dissatisfaction after TKA. In future study, more biomechanical parameters should be evaluated to find meaningful dissatisfying factor after TKA. Conclusion. In conclusion, TKA musculoskeletal models of squat and gait motion were constructed and patellofemoral contact force / hamstring to quadriceps force ratio were evaluated. Patellofemoral mechanics were validated by comparison of previous study. Additional studies are needed to find dissatisfying factor after TKA

Introduction. Currently, knee and hip implants are evaluated experimentally using mechanical simulators or clinically using long-term follow-up. Unfortunately, it is not practical to mechanically evaluate all patient and surgical variables and predict the viability of implant success and/or performance. More recently, a validated mathematical model has been developed that can theoretically simulate new implant designs under in vivo conditions to predict joint forces kinematics and performance. Therefore, the objective of this study was to use a validated forward solution model (FSM) to evaluate new and existing implant designs, predicting mechanics of the hip and knee joints. Methods. The model simulates the four quadriceps muscles, the complete hamstring muscle group, all three gluteus muscles, iliopsoas group, tensor fasciae latae, and an adductor muscle group. Other soft tissues include the patellar ligament, MCL, LCL, PCL, ACL, multiple ligaments connecting the patella to the femur, and the primary hip capsular ligaments (ischiofemoral, iliofemoral, and pubofemoral). The model was previously validated using telemetric implants and fluoroscopic results and is now being used to analyze multiple implant geometries. Virtual implantation allows for various surgical alignments to determine the effect of surgical errors. Furthermore, the model can simulate resecting, weakening, or tightening of soft tissues based on surgical errors or technique modifications. Results. The model revealed PCL weakening leads to paradoxical anterior slide of both femoral condyles. This paradoxical slide reduces maximum flexion and increases knee forces as seen in TKA fluoroscopic studies. Cam/post kinematics in posterior-stabilized designs were also analyzed, revealing cam/post forces increasing linearly with flexion. While cam/post engagement should ideally occur superiorly on the post and move inferiorly throughout knee flexion, fluoroscopy documented implants contacting inferiorly and rolling superiorly with flexion. Thus, a theoretical new implant was simulated to overcome this problem such that TKA design would experience the desired motion, yielding inferior contact in later flexion when forces approach 1.0 × BW. At the hip, the model predicts maximum compressive hip forces of 1.5–2.5 xBW throughout stance phase of gait. The model determines how this force is distributed on the femoral head and acetabular cup throughout the entire activity, allowing wear patterns on implant components to be predicted. During stance phase, the model predicts posterior-to-anterior sliding of the femoral head, with larger magnitudes of motion occurring on the supero-lateral aspect of the cup. The model can predict femoral neck impingement on the acetabular cup and shows that excessive anteversion of the cup leads to the femoral component levering away from the acetabular cup, yielding up to 2.0 mm of hip separation. Conclusions. This study demonstrates the ability of an in-vivo data based forward solution model to evaluate the impact of variation upon implant forces, motion and performance. This will improve understanding of observations such as polyethylene wear, pain associated with excessive soft-tissue forces, subluxation and dislocation, among others. Ultimately, the model could become a theoretical simulator that could evaluate implants much quicker for longer time durations, be less costly and provide comparative analyses when compared to present day experimental simulators

Introduction. Restoration of knee function after total knee arthroplasty (TKA) often entails a balance between normal kinematics and normal knee stability, especially in performing demanding physical activities. The ultra-congruent (UC) knee design prioritizes stability over kinematics through close conformity between the femoral component and the tibial insert in extension. This configuration is intended to provide AP stability in the absence of the posterior cruciate ligament during activities that would otherwise cause anterior femoral subluxation. In this study we examine the kinematics of an ultra-congruent knee design in comparison with the intact knee and with conventional articulations used in PCL-retaining (CR) and PCL-substituting (PS) TKR designs. Materials and Methods. The 3D tibio-femoral kinematics of 6 fresh frozen cadaveric human knees were tested during loaded simulation of squatting in a computer-controlled knee testing rig. Muscle forces were simulated by loading rectus femoris and vastus intermedius (150N), vastus lateralis (100N), vastus medialis (75N), and the hamstring muscles (60N) (total: 385N). Testing was performed on the intact knee, and after implanting a standard design of total knee prosthesis with the posterior cruciate ligament intact (CR-TKA), resected (PCL-substituting insert; PS-TKA), and a UC insert (UC-TKA group). The 3D positions of the tibia and femur were tracked with a high resolution 12 camera motion analysis system (Motion Analysis Inc.) and used to position 3D CT reconstructions of each bone. The translation and rotation of the femur with respect to the tibia were calculated by projecting the femoral transcondylar axis onto a plane normal to the longitudinal anatomical axis of the tibia coincident with the transverse axis of the tibial plateau. Results. In full extension, the femur was displaced posteriorly by 14.2 ±7.0 mm compared to the intact knee (p<0.01). There was minimal posterior translation (±3mm) of the medial condyle with all 3 inserts designs, and minimal (0–3mm) translation of the lateral condyle from 0–90 degrees with both the UC and PS inserts. From 0–30 degrees flexion, the femoral component translated anteriorly by approx. 5mm without axial rotation. Beyond 30 degrees, the tibia rotated internally by a total of 11 degrees (30–120degs). This was associated with approx. 5mm of rollback of the lateral condyle and 5mm of anterior translation of the medial condyle. There was significant difference in tibial rotation between the UC-TKA group and the intact knee group (p<0.01 in UC-TKA group at 15, 30, 45, and 60°). The rotation patterns of the three designs of TKA were similar during flexion from 0–120 degrees. This was markedly different than the intact knees. Conclusions. The UC TKA demonstrated minimal AP translation with flexion averaging approx. 6mm of posterior rollback laterally, and 3mm of anterior translation medially from 0–120 degrees. This differential translation was associated with 9degrees of internal rotation pattern, similar to that of the PS insert. The clinical success of the UC design and its popularity with patients as an alternative to the PS-TKA suggests that AP stability in extension, and not posterior rollback in flexion, is a critical element in patient satisfaction after TKR

Purpose. The authors have used the Edinburgh Visual Gait Score (VGS) in the management of diplegic cerebral palsy patients treated with Botulinum toxoid injections into their hamstrings muscles. Video-filmed gait episodes were recorded before and after Botox injections over a treatment period of 6 years from 2007 to 2012. Method. The video-recordings of 32 patients were available for VGS analysis. Ages ranged from 5 to 22 years, with 17 patients under the age of 12 years, and 15 over 12 years. Gross Motor Function Classification System (GMFSC) levels were accorded to: 8 patients level 1, 10 patients level 2, and 14 patients level 3; 15 were boys and 17 girls. The indication for hamstring injections were a GMFCS level of 1 to 3, age five years or older, no previous hamstring surgery, and a patient keen to have the Botox treatment. Video-recordings were taken with a Sony and a Canon Digital camera in a back-front-back view and a lateral left-right view; walking distance ap was 10 metres, lateral camera distance 5 metres. All injections of Botox were done by the senior author without anaesthetic or sedation. All assessments were done by the junior authors; they did not know the patients, the status before or after injections or repeat injections, or the dates of injections and filming of the episodes. Results. After the Botox injections into the hamstrings bilaterally, no patient changed GMFCS level status, nobody deteriorated; all could be classified in the GMFCS. Conclusion. The Edinburgh VGS is a reliable analysis method for classifying GMF levels in diplegic walking cerebral palsy patients. Video-recordings are permanent and can repeatedly be re-assessed in future; different visual parameters may be chosen for assessment. ONE DISCLOSURE

Hamstring muscle strain is a common sports related injury. It has been reported in a variety of sports, following acceleration or deceleration while running or jumping. Injury may vary from simple muscle strains to partial or complete rupture of the hamstring origin. Avulsion fracture of the ischial tuberosity has also been described. Simple hamstring muscle strains are treated conservatively. Surgical exploration and repair is currently advocated for partial or complete rupture of the hamstring origin. A few case series exists in literature suggesting the benefits of early intervention. We report a series of 8 athletes who presented between 2002 and 2006 with complete tear of their hamstring origin. Avulsion of the ischial tuberosity was excluded in these cases. After confirming the diagnosis, early surgical exploration and repair or reattachment was performed. The patients were braced for 8 weeks. This was followed by specialist physiotherapy and a supervised rehabilitation programme over 6 months. All patients were followed up to monitor return to normal activities and sports. The sciatic nerve was scarred to the avulsed tendon in three cases. Neurolysis led to a rapid relief of symptoms. Cases where the hamstring origin had retracted more than 3 cm required a figure 7 incision. There were no major complications including nerve palsies. An excellent functional outcome was noted by 12 months in all 8 patients. 7 of them returned to their previous level within 6-9 months of injury. One person despite a very good recovery, opted out of sports. No other complications were seen as a result of the surgical procedure. In conclusion, a tear of the origin of hamstring muscles is a significant injury. Early surgical repair and physiotherapy is associated with a good outcome and enables an early return to high level sports

INTRODUCTION. Total knee arthroplasty (TKA) is a very successful procedure with good clinical outcomes. However, the effects of obesity on TKA outcomes remain controversial and inconclusive. The objective of this study was to quantify the biomechanical effects of simulated obesity on Cruciate Retaining (CR) and Posterior Stabilized (PS) TKA in human cadaveric knees. We hypothesized that biomechanical characteristics of CR TKA will be less dependent on simulated obesity compared to PS TKA. METHODS. Eight cadaveric knees (4 male, 4 female) average age 68.4 years (range, 40–86 years) underwent TKA and were tested using a custom knee testing system. Specifically, Cruciate Retaining (CR) and Posterior Stabilized (PS) Lospa Knee System (Corentec Inc.) were implanted and tested sequentially using internal control experimental design. The muscle loading was determined based on the physiological cross-sectional area ratio of the quadriceps and hamstring muscles. The ratios were then applied to CDC data representing the average male height and used to simulate a BMI of 25, 30, and 35 at knee flexion angles (KFA) of 15, 30, 45, 60, 75, and 90 degrees. Patellofemoral and tibiofemoral joint contact areas and pressures were measured using the K-scan sensor system (Tekscan Inc, South Boston, MA). Contact area, force, pressure and peak contact pressure were obtained and analyzed for each specimen. Knee kinematics were quantified using a Microscribe 3DLX digitizer (Revware Inc, Raleigh, North Carolina). Repeated measure analysis of variance with a Tukey post hoc test was used to compare loading conditions. Comparisons between the CR and PS TKA groups were made with a paired t-test. The significance level was set at 0.05. RESULTS. At higher KFAs, the tibia position in the CR knees was more anterior relative to the femur than in the PS design (p<0.5). The greatest effect was seen at 90 KFA and a BMI of 25 with the tibia being 4.7 mm further anterior in the CR knees compared to the PS knees. The PS knees showed a greater anterior translation with increasing BMI at higher KFAs (Fig 1). Tibial rotation was unaffected by an increase in BMI through all flexion angles, regardless of implant type. The CR knees had greater tibiofemoral forces at higher KFA compared to the PS for all BMI levels. From 15 to 60 KFA, the lateral tibiofemoral pressures in the CR knee demonstrated greater increases as the BMI increased, however, this was only statistically significant at 60 KFA. At higher KFA, there was a significantly higher patellofemoral force in the PS knee compared to the CR knee. There was a significant increase in patellofemoral contact area for PS knees vs. CR knees. The CR knee showed significantly greater percent change in peak pressures with an increase in BMI from 25 to 35 in mid flexion (Fig 2). CONCLUSION. Tibia kinematics with CR TKA were less dependent to increased muscle loading simulating increased BMI compared to PS TKA; however patellofemoral and tibiofemoral contact pressure showed larger changes with increased BMI for the CR TKA compared to the PS TKA

Given their role in reducing anterior tibial translation, the recruitment patterns and viscoelastic properties of the hamstring muscles have been implicated as neuromuscular factors contributing to the ACL gender bias. Nevertheless, it is uncertain whether patterns of aberration displayed by the female neuromuscular system significantly alters the antagonist moments generated by the hamstrings during maximal effort knee extension. The purpose of the current study was to examine the effect of gender on hamstring antagonist moments in order to explain the higher ACL injury rates in females. Eleven females (age 30.6 ± 10.1 years, mass 62.1± 6.9 kg, height 165.9 ± 4.6) and 11 males (age 29.0 ± 8.2 years, mass 78.6± 14.4 kg, height 178.5± 6.2) were recruited as subjects. Surface electrodes were placed over the semitendinosus (ST) and biceps femoris (BF) muscles of the dominant and non-dominant limbs. Each subject performed two sets of five maximal extension and flexion repetitions at 180-1. EMG, isokinetic torque and knee displacement data were sampled at 1000Hz using an AMLAB data acquisition system. Average hamstring antagonist torque data across the range of knee flexion for female subjects was significantly higher (%Diff=24%) than for the male control subject. Statistical analyses revealed a significant main effect of gender (F = 4.802; p = 0.036). Given that females possess a more compliant ACL and hamstring musculature, compared with their male counterparts, an augmented hamstring antagonist may represent a compensatory neuromuscular strategy to increase knee stiffness to control tibial translation and ACL strain. The results of this project suggest that it is unlikely that gender-related differences in hamstring antagonist torque is one of the predisposing factors contributing to the higher ACL injury rates in females

Introduction. Increasing attention to the functional outcome of total knee arthroplasty (TKA) has demonstrated that many patients experience limitations when attempting to perform demanding activities that are normal for age-matched peers, primarily because of knee symptoms. Episodes of instability following TKA are most commonly reported during activities in which significant transverse or torsional forces are supported by the joint with relatively low joint compression forces, including stair-descent and walking on sloped or uneven surfaces. This study was performed to examine the influence of conformity between the femoral and tibial components on the Antero-Posterior (AP) stability of knee during stair descent. Methods. Six cadaveric knees were loaded in a six degree-of-freedom joint simulator, with the application of external forces simulating the action of the quadriceps and hamstring muscles and the external loads and moments occurring during stair descent, including the stages of terminal swing phase, weight-acceptance phase (prior to and after quadriceps contraction) and mid-stance. During these manoeuvres, the displacement and rotation of the femur and the tibia were measured with a multi-camera high resolution motion analysis system (Fig. 1). Each knee was tested in the intact and ACL deficient condition – and after implantation of total knee prosthesis with Cruciate-Retaining (CR), Cruciate-Sacrificing with an intact PCL (CS + PCL), Cruciate-Sacrificing with an absent PCL (CS-PCL) and Posterior-Stabilizing (PS) tibial inserts (Figs 2 and 3). Results. Loading of the knee during stair descent caused the femur to displace anteriorly by 4.31 ± 1.47 mm prior to quadriceps contraction. After TKA, anterior displacement ranged from 1.11 ± 0.41 mm (PS) to 8.19 ± 3.17 mm (CS-PCL). Intermediate values were 1.46 + 0.42 mm (CS + PCL) and 3.03 ± 0.94 mm (CR). Quadriceps contraction was able to restore the femoral AP position (5.53 ± 1.08 mm posterior motion) in the intact knee, but larger quadriceps force were required for the other designs (8.22 ± 2.94 mm CS-PCL, 2.32 ± 0.83 mm CS + PCL, 2.02 ± 0.94 mm CR design, and 1.08 ± 0.38 mm with the PS. Conclusion. Pain during high demand activities such as stair descent is a common complaint of patients after TKA, and this may be due to AP instability and extra-physiologic quadriceps demand. The only designs that restored anterior-posterior knee stability were a PS insert or a CS insert with an intact PCL. The CS design without a PCL demonstrated the worst AP stability, despite the fact that these inserts are designed to be used without a PCL

Orthopaedic companies spend years and millions of dollars developing and verifying new total knee arthroplasty (TKA) designs. Recently, computational models have been used in the hopes of increasing the efficiency of the design process. The most popular predictive models simulate a cadaveric rig. Simulations of these rigs, although useful, do not predict in vivo behavior. Therefore, in this current study, the development of a physiological forward solution, or predictive, rigid body model of the knee is described. The models simulate a non-weight bearing extension activity or a weight-bearing deep knee bend (DKB) activity. They solve for both joint forces and kinematics simultaneously and were developed from the ground up. The models are rigid body and use Kane's dynamical equations. The model began with a simple two dimensional non-weight bearing extension activity model of the tibiofemoral joint. Step by step the model was expanded. Quadriceps and hamstring muscles were added to drive the motion. Ligaments were added represented by multiple non-linear spring elements. The model was expanded to three-dimensions (3D) allowing out of plane motions and calculation of medial and lateral condylar forces. The patella was added as its own body allowing for simulation of the patellofemoral joint. The model was then converted to a weight bearing deep knee bend activity. A pelvis and trunk were added and muscles were given physiological origin and insertion points. A modified proportional-integral-derivative (PID) controller was implemented to control the rate of flexion and also to assist in joint stability by adjusting the force in individual quadriceps muscles. A method for representing articulating geometry was developed. Once the deep knee bend model was fully developed (Figure 1) it was converted back to a non-weight bearing extension model (Figure 2) resulting in simulations of a normal knee performing a weight bearing and non-weight bearing activity. The tibiofemoral kinematic results were compared to in vivo kinematics obtained from a fluoroscopy study of five normal subjects. Parameters from the CT models of one of these subjects (Subject 3) were used in the model. The model kinematics behave as the normal knee does in vivo. The kinetic results were within reasonable ranges with a maximum total quadriceps force of 0.86 BW and 4.73 BW for extension and DKB simulations, respectively (Figure 3 and Figure 4). The maximum total tibiofemoral forces were 1.26 BW and 3.70 BW for extension and DKB, respectively. The relationship between the quadriceps force, patella ligament force and patellofemoral forces are consistent with how the extensor mechanism behaves (Figure 3 and Figure 4). The patellofemoral forces are low between 0 and 20 degrees flexion and the patella ligament and quadriceps forces are close in magnitude from 0 to around 70 degrees flexion when the patellofemoral forces increase and the quadriceps forces increase relative to the patella ligament force. The model allows for virtual implantation of TKA geometry and after kinematic and kinetic validation from in vivo TKA data can be used to predict the behavior of TKA in vivo

Purpose. Whether the presence of knee effusion in individuals with knee osteoarthritis (OA) affects periarticular neuromuscular control during gait and thus the joint loading environment is unknown. The purpose was to test the hypothesis that knee effusion presence alters periarticular neuromuscular patterns during gait in individuals with moderate knee OA. Method. 40 patients with medial compartment knee OA participated after giving informed consent. Patients were assessed for the presence of effusion using a brush test and were assigned to the knee effusion (n=20) and no knee effusion (n=20) groups. Surface electrodes were placed in a bipolar configuration over the lateral and medial gastrocnemius, vastus lateralis and medialis, rectus femoris and the lateral and medial hamstrings of the affected limb. Five trials of self-selected walking were completed. Electromyograms (EMG) were collected using an AMT-8 EMG system (Bortec Inc.). An Optotrak motion capture system (Northern Digital Inc.) recorded leg motion. Euler rotations were used to derive knee angles. EMG waveforms were low-pass filtered and amplitude normalized to maximal effort voluntary isometric contractions. Quadriceps, gastrocnemius and hamstring strength was measured from torques produced against a Cybex dynamometer. Principal Component Analysis extracted the predominant waveform features and weighting scores were calculated for each measured waveform. Analysis of variance models test for main effects (group, muscle) and interactions (alpha = 0.05). Bonferonni post hoc testing was employed. Results. No differences in age, body mass index, knee pain, Western Ontario McMaster Osteoarthritis Index scores, gait velocity and muscle strength were found between groups (p>0.05). Gastrocnemius activation was not influenced by the presence of effusion (p>0.05). For individuals with effusion, a greater overall quadriceps activation was found and a prolonged hamstring activation into mid-stance only (p<0.05). Range of motion excursion from heel strike to peak extension during terminal stance was greater with effusion (p<0.05). Conclusion. The hypothesis that knee effusion in those with moderate knee OA is associated with alterations in quadricep and hamstring muscle activation patterns and sagittal plane knee motion during gait was supported. Quadriceps muscle inhibition during the normalization exercises may provide a partial explanation, consistent with results from acute effusion models. However, the hamstring alteration during mid-stance only, no strength differences between the two groups and altered kinematics support that mechanisms other than muscle inhibition are responsible for the altered patterns. These novel findings are a first step at understanding the effects of knee effusion on periarticular muscle function during gait that subsequently can affect the mechanical environment of the joint in those with a more chronic effusion

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. Knee contact force during activities after total knee arthroplasty (TKA) is very important, since it directly affects component wear and implant loosening. While several computational models have predicted knee contact force, the reports vary widely based on the type of modeling approach and the assumptions made in the model. The knee is a complex joint, with three compartments of which stability is governed primarily by soft tissues. Multiple muscles control knee motion with antagonistic co-contraction and redundant actions, which adds to the difficulty of accurate dynamic modeling. For accurate clinically relevant predictions a subject-specific approach is necessary to account for inter-patient variability. METHODS. Data were collected from 3 patients who received custom TKA tibial prostheses instrumented with force transducers and a telemetry system. Knee contact forces were measured during squatting, which was performed up to a knee flexion angle that was possible without discomfort (range, 80–120°). Skin marker-based video motion analysis was used to record knee kinematics. Preoperative CT scans were reconstructed to extract tibiofemoral bone geometry using MIMICS (Materialise, Belgium). Subject-specific musculoskeletal models of dynamic squatting were generated in a commercial software program (LifeMOD, LifeModeler, USA). Contact was modeled between tibiofemoral and patellofemoral articular surfaces and between the quadriceps and trochlear groove to simulate tendon wrapping. Knee ligaments were modeled with nonlinear springs: the attachments of these ligaments were adjusted to subject-specific anatomic landmarks and material properties were assigned from published reports. RESULTS. Total measured peak ground reaction force was 0.9–1.1 xBW (times of bodyweight) and measured peak knee contact force was 2.2 (±0.2) xBW during squatting. Model predicted peak tibiofemoral contact forces were within the cycle-to-cycle variations for each subject. Model predicted peak patellofemoral contact forces were 0.9–1.1 xBW and peak quadriceps forces were 1.3–1.6 xBW. Mean peak ligament tensions were 55.5 ± 8.8 N for the MCL and 47.1 ± 10.4 N for the LCL. DISCUSSION. Small differences between predicted and measured forces were likely due to the complexity of the squatting activity, the inherent error in skin marker-based motion capture, and the fact that muscle force was computed from muscle shortening history. Trunk flexion significantly affected the contact force, especially at higher knee flexion angles. Trunk flexion reduced the external flexion moment at the knee leading to reduced quadriceps force and therefore reduced tibiofemoral contact force. Peak patellofemoral contact forces and quadriceps muscle forces were also lower than previously reported. Although others have reported on hamstring muscle activity during the squat, hamstring forces were low in our models in qualitative agreement with the EMG data that we recorded during squatting. The lack of significant hamstring activity may explain the lower net tibiofemoral contact forces. This model would be very useful tool to predict the effect of surgical techniques on contact forces. Such a model could be used for implant design development to enhance knee function and to predict forces generated during other activities. Finally a subject-specific model could be useful for predicting clinical outcomes

We present a retrospective review of a single-surgeon series of 30 consecutive lengthenings in 27 patients with congenital short femur using the Ilizarov technique performed between 1994 and 2005.

The mean increase in length was 5.8 cm/18.65% (3.3 to 10.4, 9.7% to 48.8%), with a mean time in the frame of 223 days (75 to 363). By changing from a distal to a proximal osteotomy for lengthening, the mean range of knee movement was significantly increased from 98.1° to 124.2° (p = 0.041) and there was a trend towards a reduced requirement for quadricepsplasty, although this was not statistically significant (p = 0.07). The overall incidence of regenerate deformation or fracture requiring open reduction and internal fixation was similar in the distal and proximal osteotomy groups (56.7% and 53.8%, respectively). However, in the proximal osteotomy group, pre-placement of a Rush nail reduced this rate from 100% without a nail to 0% with a nail (p < 0.001). When comparing a distal osteotomy with a proximal one over a Rush nail for lengthening, there was a significant decrease in fracture rate from 58.8% to 0% (p = 0.043).

We recommend that in this group of patients lengthening of the femur with an Ilizarov construct be carried out through a proximal osteotomy over a Rush nail. Lengthening should also be limited to a maximum of 6 cm during one treatment, or 20% of the original length of the femur, in order to reduce the risk of complications.