Aims

To fully quantify the effect of posterior tibial slope (PTS) angles on joint kinematics and contact mechanics of intact and anterior cruciate ligament-deficient (ACLD) knees during the gait cycle.

Aims

Improvements in the evaluation of outcomes following peripheral nerve injury are needed. Recent studies have identified muscle fatigue as an inevitable consequence of muscle reinnervation. This study aimed to quantify and characterize muscle fatigue within a standardized surgical model of muscle reinnervation.

Objectives

Unicompartmental knee arthroplasty (UKA) is one surgical option for treating symptomatic medial osteoarthritis. Clinical studies have shown the functional benefits of UKA; however, the optimal alignment of the tibial component is still debated. The purpose of this study was to evaluate the effects of tibial coronal and sagittal plane alignment in UKA on knee kinematics and cruciate ligament tension, using a musculoskeletal computer simulation.

Aims

In patients with a rotator cuff tear, tear pattern and tendon involvement are known risk factors for the development of pseudoparalysis of the shoulder. It remains unclear, however, why similar tears often have very different functional consequences. The present study hypothesizes that individual shoulder anatomy, specifically the moment arms (MAs) of the rotator cuff (RC) and the deltoid muscle, as well as their relative recruitment during shoulder abduction, plays a central role in pseudoparalysis.

Aims

Tibiofemoral alignment is important to determine the rate of progression of osteoarthritis and implant survival after total knee arthroplasty (TKA). Normally, surgeons aim for neutral tibiofemoral alignment following TKA, but this has been questioned in recent years. The aim of this study was to evaluate whether varus or valgus alignment indeed leads to increased medial or lateral tibiofemoral forces during static and dynamic weight-bearing activities.

Introduction. Preservation of the anterior cruciate ligament (ACL), along with the posterior cruciate ligament, is believed to improve functional outcomes in total knee replacement (TKR). The purpose of this study was to examine gait differences and muscle activation levels between ACL sacrificing (ACL-S) and bicruciate retaining (BCR) TKR subjects during level walking, downhill walking, and stair climbing. Methods. Ten ACL-S (Vanguard CR) (69±8 yrs, 28.7±4.7 kg/m2) and eleven BCR (Vanguard XP, Zimmer-Biomet) (63±11 yrs, 31.0±7.6 kg/m2) subjects participated in this IRB approved study. Except for the condition of the ACL, both TKR designs were similar. Subjects were tested 8–14 months post-op in a motion analysis lab using a point cluster marker set and surface electrodes applied to the Vastus Medialis Oblique (VMO), Rectus Femoris (RF), Biceps Femoris (BF) and Semitendinosus (ST). 3D motion and force data and electromyography (EMG) data were collected simultaneously. Subjects were instructed to walk at a comfortable walking speed across a walkway, down a 12.5% downhill slope, and up a staircase. Five trials per activity were collected. Knee kinematics and kinetics were analyzed using BioMove (Stanford, Stanford, CA). The EMG dataset underwent full-wave rectification and was smoothed using a 300ms RMS window. Gait cycle was time normalized to 100%; relative voluntary contraction (RVC) was calculated by dividing the average activation during downhill walking by the maximum EMG value during level walking and multiplying by 100%. Results. There were no significant kinematic or kinetic differences between implant groups for level walking (p≥0.19). Both groups walked at 1.1 m/s on average during level and approximately 0.1 m/s slower during downhill walking, with no differences in speed (p= 0.91 and 0.77, respectively). For both ACL-S and BCR groups, gait changes from level to downhill walking were similar. For downhill walking, ACL-S subjects were significantly more variable (p<0.001) over the gait cycle for all measured kinematics and kinetics. During both downhill walking and stair climbing, the ACL-S group showed an external peak abduction moment (Fig. 1) significantly greater than that of the BCR group (p=0.05, 0.01). Also during stair climbing, ACL-S subjects showed trending higher peak knee adduction moments (p=0.14) and a more pronounced internal/external rotation pattern (Fig. 2) than BCR subjects. Since no peak kinematic/kinetic differences between groups during level walking exist, the mean maximum muscle activation from level walking was used for RVC normalization for other activities. On average, BCR subjects had lower maximum RVCs during downhill walking than the ACL-S subjects. Effect sizes were large for RF (d=0.94), ST (d=0.88), and VMO (d=1.21), the latter being borderline significant (p=0.05). Discussion. Previous studies on the natural knee have established that the ACL contains mechanoreceptors that improve stability of the knee joint. In this study, BCR subjects show less variable gait measures than subjects with traditional posterior cruciate retaining (ACL-S) TKR, possibly indicating more controlled contact kinematics. In addition, EMG results suggest lower muscle co-contraction during downhill walking, also implying greater knee stability in the BCR group. These results are preliminary and more subjects are needed for definite conclusions

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

In total knee replacement (TKR), neutral mechanical alignment (NMA) is targeted in prosthetic component implantation. A novel implantation approach, referred to as kinematic alignment (KA), has been recently proposed (Eckhoff et al. 2005). This is based on the pre-arthritic lower limb alignment which is reconstructed using suitable image-based techniques, and is claimed to allow better soft-tissue balance (Eckhoff et al. 2005) and restoration of physiological joint function. Patient-specific instrumentation (PSI) introduced in TKR to execute personalized prosthesis component implantation are used for KA. The aim of this study was to report knee kinematics and electromyography (EMG) for a number lower limb muscles from two TKR patient groups, i.e. operated according to NMA via conventional instrumentation, or according to KA via PSI. 20 patients affected by primary gonarthrosis were implanted with a cruciate-retaining fixed-bearing prosthesis with patella resurfacing (Triathlon® by Stryker®, Kalamazoo, MI-USA). 17 of these patients, i.e. 11 operated targeting NMA (group A) via convention instrumentation and 6 targeting KA (group B) via PSI (ShapeMatch® by Stryker®, Kalamazoo, MI-USA), were assessed clinically using the International Knee Society Scoring (IKSS) System and biomechanically at 6-month follow-up. Knee kinematics during stair-climbing, chair-rising and extension-against-gravity was analysed by means of 3D video-fluoroscopy (CAT® Medical System, Monterotondo, Italy) synchronized with 4-channel EMG analysis (EMG Mate, Cometa®, Milan, Italy) of the main knee ad/abductor and flexor/extensor muscles. Knee joint motion was calculated in terms of flex/extension (FE), ad/abduction (AA), and internal/external rotation (IE), together with axial rotation of condyle contact point line (CLR). Postoperative knee and functional IKSS scores in group A were 78±20 and 80±23, worse than in group B, respectively 91±12 and 90±15. Knee motion patterns were much more consistent over patients in group B than A. In both groups, normal ranges were found for FE, IE and AA, the latter being generally smaller than 3°. Average IE ranges in the three motor tasks were respectively 8.2°±3.2°, 10.1°±3.9° and 7.9°±4.0° in group A, and 6.6°±4.0°, 10.5°±2.5° and 11.0°±3.9° in group B. Relevant CLRs were 8.2°±3.2°, 10.2°±3.7° and 8.8°±5.3° in group A, and 7.3°±3.5°, 12.6°±2.6° and 12.5°±4.2° in group B. EMG analysis revealed prolonged activation of the medial/lateral vasti muscles in group A. Such muscle co-contraction was not generally observed in all patients in group B, this perhaps proving more stability in the knee replaced following the KA approach. These results reveal that KA results in better function than NMA in TKR. Though small differences were observed between groups, the higher data consistency and the less prolonged muscle activations detected using KA support indirectly the claim of a more natural knee soft tissue balance. References

Aims

Improvements in the evaluation of outcome after nerve transfers are required. The assessment of force using the Medical Research Council (MRC) grades (0 to 5) is not suitable for this purpose. A ceiling effect is encountered within MRC grade 4/5 rendering this tool insensitive. Our aim was to show how the strength of flexion of the elbow could be assessed in patients who have undergone a re-innervation procedure using a continuous measurement scale.

Summary. This study describes the use of a quasi-static, 6DOF knee loading simulator using cadaveric specimens. Muscle force profiles yield repeatable results. Intra-articular pressure and contact area are dependent on loading condition and ACL integrity. Introduction. Abnormal contact mechanics of the tibiofemoral joint is believed to influence the development and progression of joint derangements. As such, understanding the factors that regulate joint stability may provide insight into the underlying injury mechanisms. Muscle action is believed to be the most important factor since it is the only dynamic regulator of joint stability. Furthermore, abnormal muscle control has been experimentally linked to the development of OA [Herzog, 2007] and in vivo ACL strain [Fleming, 2001]. However, the individual contributions to knee joint contact mechanics remain unclear. Thus, the purpose of this study was to examine the effects of individual muscle contributions on the tibiofemoral contact mechanics using an in-vitro experimental protocol. Methodology. Contact mechanics of 6 fresh frozen cadaver knee specimens were evaluated using the UofO Oxford knee loading device. Various combinations of quadriceps-hamstring co-contraction ratios were applied to the knee while it was “suspended” between the hip and foot components of the device. Loads of six muscle groups were computed using a hill-type musculoskeletal model [Buchanan, 2004]. Simulated ground reaction forces were also applied to the knee to represent force profiles of weight acceptance during gait as it has been shown to produce peak knee joint force in the gait cycle [Shelburne et al., 2006]. For respective medial and lateral joint compartments, the mean contact area (MC-CA and LC-CA), mean contact pressure (MC-CP and LC-CP), peak pressure (MC-PP and LC-PP), and centre of force displacement (MC-COFD and LC-COFD) were determined using a 4011 piezoelectric sensor form Tekscan (Tekscan Inc. Boston, MA). Additionally, the ACL was resected and measurements were repeated. Pearson correlations (r) examined the reliability of measurements as well as the effect an ACL transection on articular loads. Results. Positive correlations were computed for the following: COFD with intact ACL (r=0.99), COFD with resected ACL (r=0.82), MC-COFD pre vs. post ACL- resection (0.91). Furthermore, preliminary results indicated a positive correlation between MC-CA and ACL integrity (r=0.97). Discussion. The repeatability of the measured dependant variables validates the use of the knee-loading device. Interestingly, contact mechanics are more variable post ACL resection for a given muscle loading condition, indicating a decrease in knee joint stability. Also, the COFD is dependent on the different ratios of muscle loads applied to the knee, which demonstrates the importance of muscle action to the modulation of contact forces

Summary Statement. Using a weight-bearing force control task, age-related changes in muscle action were observed in osteoarthritic subjects, however, greater activation of rectus femoris and medial hamstring muscles in the OA group compared to control indicates greater cocontraction and varied stabilisation strategies. Introduction. Osteoarthritis (OA) is the most debilitating condition among older adults. OA is thought to be mechanically driven by altering the stabilising integrity of the joint. The main contributor to knee joint stability is that of muscular contraction. In cases where the history of a traumatic knee joint injury is not a causal factor, a change in muscle function, resulting in reduced strength and force control in believed to induce OA development and progression. Since age is also a determining factor of OA, the purpose of this study was to investigate the muscle activation patterns of young healthy adults (YC), older healthy adults (OC), and adults with OA during a standing isometric force control task. Patients & Methods. A force matching protocol was used to evaluate muscle activation patterns of 41 YC (23.1±1.9 years of age) 18 OC (59.7±5.14 years), and 19 OA (63.5±8.1 years). Subjects stood with their leg of interest fixed to a force platform and modulated ground reaction forces while exposing equal body weight to each leg. Surface electromyography (EMG) of 8 muscles that cross the knee joint, kinetics and kinematics were recorded while subjects generated 30% of their maximal force in 12 different directions, corresponding to various combinations of medial-lateral-anterior-posterior ground reaction forces. Processed EMG was normalised to previously recorded maximum voluntary isometric contraction (MVIC) and ensemble averaged into group means for each loading direction. Muscle activation patterns were displayed in EMG polar plots and were quantified with symmetry analyses, mean activation levels (X. EMG. ), directions (Φ), and specificity indices (SI). Group differences were tested with independent T-tests at the p<0.05 level. Results. Muscle activation patterns were similar between groups (i.e. symmetry and Φ). However, X. EMG. of 7 muscles was significantly greater in both the OA and OC groups compared to YC. OA group also demonstrated significantly greater X. EMG. in the rectus femoris and tensor fascia lata as well as lower SI in semitendinosus hamstrings compared to OC. Discussion/Conclusion. Our results indicate that regardless of loading direction, both OC and OA groups have greater levels of muscle co-contraction than YC. This is suggested to be an adaptive response to age-related changes in muscle strength and force control. Since individuals with OA have reduced muscle strength and force control compared to age-matched controls, our results suggest that the OA group's greater, less specific activation of knee joint muscles relative to the OC is this “stiffening” response adapted by the OA group, however, to an extent that may expose the joint to detrimental loading conditions, contributing to the progression of OA. Further investigation regarding age-related neuromuscular changes and their influence on joint loading conditions and development of OA is warranted

Background:. It is not well known how different external loads influence shoulder kinematics and muscle activity in patients with shoulder prostheses. Study objective: define shoulder kinematics and determine the scapulothoracic contribution to total shoulder motion, in combination with shoulder muscle activity and the degree of co-contraction, of patients with total (TSA) and reverse shoulder arthroplasties (RSA) and healthy individuals during rehabilitation exercises using different loading conditions. Methods:. Shoulder motions (anteflexion and elevation in the scapular plane) of 17 patients (20 shoulders) with a TSA, 8 patients (9 shoulders) with a RSA and 15 healthy subjects were measured using anelectromagnetic tracking device. A force transducer recorded force signals during loaded conditions (without external load, 1 kg and elastic resistance). Electromyographic (EMG) activity of the deltoid (anterior, middle, posterior parts), latissimus dorsi, pectoralis major (clavicular and sternal parts), teres major and serratus anterior was recorded and the degree of co-contraction calculated. Results:. The scapula contributed more to movement of the arm in subjects with prostheses compared to healthy subjects and during loaded versus unloaded tasks. Glenohumeral elevation angles during anteflexion were significantly higher in the TSA than in the RSA group. Higher activity of the middle and posterior deltoid was found in the TSA group compared to healthy subjects and for the pectoralis major (sternal part) in the RSA group compared to TSA and healthy subjects. For all muscles, except the serratus anterior, activity was lower for unloaded tasks compared to 1 kg dumbbell and elastic band resistance. No main effect of group or load for degree of co-contraction was detected in both exercises. Conclusions:. Differences in contribution of the scapula to total shoulder motion between patients with different types of arthroplasties were not significant, but differed both compared to healthy subjects. Scapular kinematics of patients with shoulder arthroplasties were influenced by implementation of external loads, however, not by the type of load. There were no differences in muscle activity and degree of co-contraction between patient groups

Knowledge of joint kinematics in the lower limb is important for understanding joint injuries and diseases and evaluating treatment outcomes. However, limited information is available about the joint kinematics required for high flexion activities necessary for floor sitting life style. In this study, the hip and knee joint kinematics of ten healthy male and ten healthy female subjects were investigated using an electromagnetic motion tracking system. We measured the hip and knee joints' functions moving into 1) kneeling on knees with legs parallel without using arms, 2) kneeling on knees with legs parallel with using arms, 3) kneeling on knees with one foot forward without using arms, 4) cross-legged sitting, 5) kneeling with legs to the side, 6) sitting with legs stretched out, and 7) deep squatting, and moving out of the above seven conditions. Conditions 1) through 3) were Japanese seiza style. On conditions 4) through 7), arms were not used. We further measured the functions of putting on and taking off a sock under such conditions as 8) with standing position and 9) sitting position (Fig 1). Here special attention was paid for flexion and extension motion. The data were used to produce the pattern of joint angulation against the percentage of the cycle for each individual conducting each activity. The kinematic curves were split into 3 phases: moving into the rest position, the rest position and out of the rest position. It should be noted that the moving into and the rest phases were split at the moment when the peak value was determined during the moving into phase. Thus the initiation of the rest phase on the curve was not coinciding with the moment the subject reached at the rest position. This was necessary in order not for the mean kinematic curve to become too dull in shape. Same was true when the end of rest phase was determined. The maximum hip and knee joint angles during the cycle were determined. Further a relationship between the hip and knee joint excursions were investigated. The results indicated condition 8) requires the maximum flexion angles to the hip among all conditions, 157.5 ± 20.4° and condition 3) to the knee joint, 157.1 ± 10.0° respectively (Fig 2). The results also indicated in many activities, the maximum joint angles were recorded not during the rest phase but during the moving into or out of phase. In any conditions even including donning on and off a sock, a strong relationship was found between the hip and knee joints motion (Fig 3), indicating the bi-articular muscles' co-contraction during the sit to stand activities. The data presented in this study will increase the knowledge of high-flexion needs especially in non-Western cultures and provide an initial characterization of the prosthesis kinematics in high flexion

The June 2013 Oncology Roundup³⁶⁰ looks at: whether allograft composite is superior to megaprosthesis in massive reconstruction; pain from glomus tumours; thromboembolism and orthopaedic malignancy; bone marrow aspirate and cavity lesions; metastasectomy in osteosarcoma; spinal giant cell tumour; post-atomic strike sarcoma; and superficial sarcomas and post-operative infection rates.

The aim of this study was to examine the loading of the other joints of the lower limb in patients with unilateral osteoarthritis (OA) of the knee. We recruited 20 patients with no other symptoms or deformity in the lower limbs from a consecutive cohort of patients awaiting knee replacement. Gait analysis and electromyographic recordings were performed to determine moments at both knees and hips, and contraction patterns in the medial and lateral quadriceps and hamstrings bilaterally. The speed of gait was reduced in the group with OA compared with the controls, but there were only minor differences in stance times between the limbs. Patients with OA of the knee had significant increases in adduction moment impulse at both knees and the contralateral hip (adjusted p-values: affected knee: p < 0.01, unaffected knee p = 0.048, contralateral hip p = 0.03), and significantly increased muscular co-contraction bilaterally compared with controls (all comparisons for co-contraction, p < 0.01). The other major weight-bearing joints are at risk from abnormal biomechanics in patients with unilateral OA of the knee. Cite this article: Bone Joint J 2013;95-B:348–53

Introduction. Patients with knee osteoarthritis frequently complain that they develop pain in other joints due to over-loading during gait. However, there have been no previous studies examining the effect of knee arthritis on the other weight bearing joints. The aim of this study was to examine the loading of the hips and contra-lateral knee during gait in a cohort of patients pre- and post knee replacement. Methods. Twenty patients with single joint osteoarthritis awaiting knee replacement and 20 healthy volunteers were recruited. Gait analysis during level gait and at self selected speed was performed using a 12 camera Vicon motion analysis system. The ground reaction force was collected using EMG electrodes attached to the medial and lateral hamstrings and quadriceps bilaterally. Patients were invited to return 12 months post-operatively. Data was analysed using the Vicon plug-in-gait model and statistical testing was performed with SPSS v16.0 using ANCOVA to account for gait speed. Results. The mean age of the patients was 69 (range 53-82) and the controls was 70 (range 60-83). Mid-stance moments and knee adduction impulses were elevated at both hips and both knees in patients compared to normal individuals (Impulses: OA Knee=1.87Nms; opposite knee=1.46Nms; controls=0.86Nms; p<0.01) whilst peak moments were not significantly different. Muscular co-contraction was elevated in both knees compared to normal (p<0.01). Ten patients returned for follow up. Correction of varus resulted in improvements in moments at the replaced knee however recovery of moments in the other joints was variable and dependant on alignment, gait speed and their ability to mobilise their centre of mass. Conclusion. Patients with single joint knee osteoarthritis have abnormal loading of both knees and both hips, potentially leading to further disease and disability. Recovery following knee replacement is variable and dependant on limb alignment and the patient's functional recovery

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

Accurate in vivo knee joint contact forces are required for joint simulator protocols and finite element models during the development and testing of total knee replacements (Varadarajan et al., 2008.) More accurate knowledge of knee joint contact forces during high flexion activities may lead to safer high flexion implant designs, better understanding of wear mechanisms, and prevention of complications such as aseptic loosening (Komistek et al., 2005.) High flexion is essential for lifestyle and cultural activities in the developing world, as well as in Western cultures, including ground-level tasks and chores, prayer, leisure, and toileting (Hemmerich et al., 2006.) In vivo tibial loads have been reported while kneeling; but only while the subject was at rest in the kneeling position (Zhao et al., 2007), meaning that the loads were submaximal due to muscle relaxation and thigh-calf contact support. The objective of this study was to report the in vivo loads experienced during high flexion activities and to determine how closely the measured axial joint contact forces can be estimated using a simple, non-invasive model. It provides unique data to better interpret non-invasively determined joint-contact forces, as well as directly measured tiobiofemoral joint contact force data for two subjects. Two subjects with instrumented tibial implants performed kneeling and deep knee bend activities. Two sets of trials were carried out for each activity. During the first set, an electromagnetic tracking system and two force plates were used to record lower limb kinematics and ground reaction forces under the foot and under the knee when it was on the ground. In the second set, three-dimensional joint contact forces were directly measured in vivo via instrumented tibial implants (Heinlein et al., 2007.) The measured axial joint contact forces were compared to estimates from a non-invasive joint contact force model (Smith et al., 2008.). The maximum mean axial forces measured during the deep knee bend were 24.2 N/kg at 78.2° flexion (subject A) and 31.1 N/kg at 63.5° flexion (subject B) during the deep knee bend (Figure 1.) During the kneeling activity, the maximum mean axial force measured was 29.8 N/kg at 86.8° flexion (subject B.) While the general shapes of the model-estimated curves were similar to the directly measured curves, the axial joint contact force model underestimated the measured contact forces by 7.0 N/kg on average (Figure 2.) The most likely contributor to this underestimation is the lack of co-contraction in the model. The study protocol was limited in that data could not be simultaneously collected due to electromagnetic interference between the motion tracking system and the inductively powered instrumented tibial component. Because skin-mounted markers were used, kinematics may be affected by skin motion artefacts. Despite these limitations, this study presents valuable information that will advance the development of high flexion total knee replacements. The study provides in vivo measurements and non-invasive estimates of joint contact forces during high flexion activities that can be used for joint simulator protocols and finite element modeling

Introduction. Patients with knee osteoarthritis (OA) often tell us that they put extra load on the joints of the opposite leg as they walk. Multiple joint OA is common and has previously been related to gait changes due to hip OA (Shakoor et al 2002). The aim of this study was to determine whether patients with medial compartment knee OA have abnormal biomechanics of the unaffected knee and both hips during normal level gait. Methods. Twenty patients (11 male, 9 female), with severe medial compartment knee OA and no other joint pain were recruited. The control group comprised 20 adults without musculoskeletal pain. Patients were reviewed, x-rays were examined and WOMAC and Oxford knee scores were completed. A 12 camera Vicon (Vicon, Oxford) system was used to collect kinematic data (100Hz) on level walking and the ground reaction force was recorded using three AMTI force plates (1000Hz). Surface electrodes were placed over medial and lateral quadriceps and hamstrings bilaterally to record EMG data (1000Hz). Kinematics and kinetics were calculated using the Vicon ‘plug-in-gait’ model. A co-contraction index was calculated for the EMG signals on each side of the knee, representing the magnitude of the combined readings relative to their maximum contraction during the gait cycle. Statistical comparisons were performed using t-tests with Bonferroni's correction for two variables and ANOVA for more than two variables (SPSS v16). Results. The mean age of the patients was 69 (SD 8.8). Mean gait speed was 0.95m/s (study group) and 1.44m/s (control group). Peak adduction moments for the OA group [OA Knee; Unaffected Knee; Ipsilateral Hip; Contralateral Hip; in Nm/Kg(±95% CI)] were: 0.55(0.06); 0.47(0.06); 0.73(0.09); 0.73(0.08). Control values for peak moments were 0.64 (0.06) for the knee and 0.81(0.07) at the hip. Mid-stance adduction moments for the OA group (listed as before) were: 0.44(0.08); 0.33(0.06); 0.64(0.06); 0.61(0.08). Control values for mid-stance moments were 0.14(0.03) and 0.40(0.04). [OA group vs. Controls: p=NS for peak moments at all 4 joints; p<0.01 for mid-stance moments at all joints]. Co-contraction indices for hamstrings and quads, [OA knee medial; and lateral; unaffected knee medial; and lateral; control medial; and lateral; 0<X. Discussion. Although the affected subjects all had only single joint OA, abnormal moments were present in the hips and knees of both legs during normal level gait, despite the reduced gait speed of the OA cohort. Abnormal hamstring and quadriceps co-contraction occurs bilaterally in patient with single joint OA. Increased trunk sway is a recognised compensation in knee OA and may be the cause of the abnormal hip and contra-lateral knee loading found in this study. Further investigation is warranted and may lead to improvements in the long term outcome for these patients. Acknowledgement. The study was funded by the North Wales NHS Trust

Children with diplegic cerebral palsy develop progressive musculoskeletal deformities with deterioration in their gait. Multilevel surgery is a well-established treatment modality involving a combination of soft tissue lengthening and correction of bony deformities. At Bristol Royal Children's Hospital we have identified a cohort of 45 children with diplegic cerebral palsy who have undergone multilevel surgery. Video gait analysis had been performed pre-operatively and three years post-operatively. We utilised the Edinburgh Visual Gait Score (EVGS). [1]. , a validated system that allows direct comparison with gait videos taken during different periods of the patient's treatment. Seventeen measurements are taken per limb at each stage. The patients were also categorised according to the Functional Walking Score (FWS) . [2]. that assesses their level of independence. Post-operative results demonstrate a significant improvement in gait score on both the EVGS and FWS. Patients whose gait was more severely affected prior to surgery had the greatest improvement in mobility and functional scores. Patients consistently had significant improvements in hip and knee extension in stance phase, with more modest improvement in knee flexion in swing with persistent co-contraction. Both initial contact and heel lift were consistently abnormal pre-operatively, but few patients achieved a heel strike and normal heel lift post-operatively. We are proceeding with a long-term follow-up of this cohort of patients at 15 years following surgery. The combination of using detailed video gait analysis with functional assessment is a valuable tool in retrospective assessment of patients' outcome following surgery. It gives a quantitative evaluation of progression over time as well as allowing comparison with a cohort of patients to estimate the future level of functional independence