Biomechanical effects of joint line elevation in total knee arthroplasty

Background

Inadequate restoration of the knee joint line after total knee arthroplasty may lead to a poor clinical outcome. The purpose of this study was to quantitatively assess the effects of joint line elevation following total knee arthroplasty with increased joint volume on patellofemoral contact kinematics.

Methods

Six cadaveric specimens were tested. Patellofemoral contact area, contact pressure, and kinematics were measured following total knee arthroplasty with an anatomic joint line and after 4 and 8 mm of joint line elevation, at knee flexion angles of 0°, 30°, 60°, 90° and 120°. Repeated measures analysis of variance with a Tukey post hoc test with a significance level of 0.05 was used for statistical analyses.

Findings

There was a decrease in contact area with joint line elevation at flexion angles of 60°, 90° and 120° (P = 0.009–0.04). There was a significant increase in contact pressure only at 30° of knee flexion with 8 mm of joint line elevation (P = 0.004). Three of the six specimens showed inferior edge loading of the patella component following 8 mm of joint line elevation at 120° of knee flexion. The sagittal plane patellofemoral angle increased significantly with joint line elevation except for 0° knee flexion (P = 0.0002–0.02).

Interpretation

Knee joint line elevation with increased knee volume significantly affects patellofemoral contact area and kinematics and produced inferior edge loading/impingement between the patella and tibial components, this may result in loss of knee range of motion, postoperative pain, and premature component wear.     

Tibiofemoral contact mechanics with a femoral resurfacing prosthesis and a non-functional meniscus

Background

Increased contact stress with a femoral resurfacing prosthesis implanted in the medial femoral condyle and a non-functional meniscus is of concern for potential deleterious effects on tibiofemoral contact mechanics.

Methods

Peak contact pressures were determined in seven fresh frozen human cadaveric specimens using a pressure sensitive sensor placed in the medial compartment above the menisci. A knee simulator was used to test each knee in static stance positions (5°/15°/30°/45°) and through 10 dynamic knee flexion cycles (5–45°) with single body weight ground reaction force which was adjusted to the living body weight of the cadaver donor. All specimens were tested in three different conditions: untreated knee (A); flush implantation of a 20 mm resurfacing prosthesis (HemiCAP^®) in the weight bearing area of the medial femoral condyle (B); complete radial tear at the posterior horn of the medial meniscus with the femoral resurfacing device in place (C).

Findings

On average, flush device implantation resulted in no statistically significant differences when compared to the untreated normal knee. The meniscal tear resulted in a significant increase of the mean maximum peak contact pressures by 63%, 57%, and 57% (all P ? 0.05) at 15°, 30° and 45° static stance positions and 78% (P ? 0.05) through the dynamic knee flexion cycle. No significant different maximum peak contact pressures were observed at 5° stance position.

Interpretation

Although the condition of a meniscal tear without the resurfacing device could not be compared, possible effects of reduced meniscal tissue and biomechanical integrity of the meniscus must be considered in an in vivo application.     

Finite element model of the proximal femur under consideration of the hip centralizing forces of the iliotibial tract

Background

The aim of our investigations was the development of a finite element model of the hip joint under consideration of the hip centralizing forces of the iliotibial tract within different femoral neck angles and its influence to the centralizing of the femoral head to the acetabulum.

Methods

For the development of the finite element model of the femur and the iliotibial tract we utilized the program IDEAS 3D as well as the material/lengthening characteristics of the iliotibial tract. In the following step we developed a hip joint model with different centrum-collum-diaphysis-angles of 115°, 128° and 155° for determination of the IT force and the consequential force on the femoral head.

Findings

With a coxa vara the force on the femoral head in relation to the physiological centrum-collum-diaphysis-angle and the coxa valga decreased (115° = 1601 N, 128° = 2360 N, and 155° = 2422 N). On the other side the hip centralizing forces of the iliotibial tract within a coxa vara increased in comparison to 128° (physiological) and 155° (valga) (115° = 997 N, 128° = 655,5 N, and 155° = 438 N). Within a coxa valga a higher compressive force on the femoral head and with a coxa vara a decreasing compressive force on the femoral head occurred.

Interpretation

The clinical relevance consists in the predictability of an increasing or decreasing band wiring effect of the iliotibial tract in reliance to the centrum-collum-diaphysis-angle of the femoral neck and its importance for the displacement osteotomy of the growing hip.     

Biomechanical changes accompanying unilateral and bilateral use of laterally wedged insoles with medial arch supports in patients with medial knee osteoarthritis

Background

Laterally wedged insoles have controversial effect in treating medial compartment knee osteoarthritis. This study examined the effects of unilateral and bilateral use of insoles having medial arch supports and of different inclinations on the frontal plane external hip, knee, subtalar moments and pelvic alignment.

Methods

Kinetic and kinematic gait parameters were collected from 21 patients with primary medial knee osteoarthritis. The insoles' inclinations were 0, 6 and 11°, where each of the 6° and 11° was used once unilaterally and another bilaterally while the 0° was used bilaterally as a control.

Findings

The Multivariate Analysis of Variance revealed significant increase in the external subtalar eversion moment using either of the 6° or 11° laterally wedged vs the 0° non-wedged insole conditions (P = 0.003). Moreover, there were significant increases in the external eversion moment using the 11° vs the 6° insole conditions (P < 0.05). However, there were no significant differences for the remaining tested variables (P > 0.05). The bivariate correlations revealed significant negative correlations between the subtalar eversion and knee adduction moments (r = − 0.409, P = 0.000) and the subtalar eversion and hip adduction moments (r = − 0.226, P = 0.049), and positive correlation between the hip and knee adduction moments (r = 0.268, P = 0.019).

Interpretation

The non-significant reduction in the external knee adduction moment may question the efficacy of using wedged insoles having medial arch supports in treating patients with medial knee osteoarthritis. Additionally, using such insoles did not produce appreciable mechanical effects on remote articulations as the hip and pelvis.     

The role of the scapulo-thoracic and gleno-humeral joints in upper-limb motion in children with hemiplegic cerebral palsy

Background

The pathophysiology of abnormal shoulder motion in children with hemiplegic cerebral palsy is not yet well understood. The aim of this study was to compare the motion of the two principle shoulder joints in children with hemiplegic cerebral palsy and typically developing children.

Methods

10 children in each group carried out 6 tasks recorded by an optoelectronic system. The analysis protocol was based on an acromion marker cluster, a functional method to determine the gleno-humeral rotation center and different Euler sequences thus providing three dimensional thoraco-humeral, scapulo-thoracic and gleno-humeral kinematics during upper-limb motion.

Findings

In the children with hemiplegic cerebral palsy, the scapulo-thoracic joint was more protracted (P < 0.05) and tended to be more laterally rotated depending on the tasks and the degree of humeral elevation. The gleno-humeral joint was limited in elevation (P < 0.09), internal rotation (P < 0.05) and plane of elevation (P < 0.05) depending on the task. At rest, the orientation of the arm was more related to the scapular posture than to the gleno-humeral orientation, the latter which appeared to compensate the initial internal arm rotation at the beginning of the motion.

Interpretation

The scapulo-thoracic joint plays a key role in arm posture at rest and during motion but does not seem to limit arm motion. The gleno-humeral joint compensates the scapula orientation at small degrees of humeral elevation but has a reduced total range of motion. Clinical management should focus on both joints taking into account their respective roles in upper-limb motion in this population.     

Postural dependence of passive tension in the supraspinatus following rotator cuff repair: a simulation analysis

Background

Despite surgical advances, repair of rotator cuff tears is associated with 20–70% incidence of recurrent tearing. The tension required to repair the torn tendon influences surgical outcomes and may be dependent on the gap length from torn tendon that must be spanned by the repair. Detailed understanding of forces throughout the range of motion (ROM) may allow surgeons to make evidence-based recommendations for post-operative care.

Methods

We used a computational shoulder model to assess passive tension and total moment-generating capacity in supraspinatus for repairs of gaps up to 3 cm throughout the shoulder (ROM).

Findings

In 60° abduction, increased gap length from 0.5 cm to 3 cm caused increases in passive force from 3 N to 58 N, consistent with those seen during clinical repair. For reduced abduction, passive forces increased substantially. For a 0.5 cm gap, tension throughout the ROM (elevation, plane of elevation, and rotation) is within reasonable limits, but larger gaps are associated with tensions that markedly exceed reported pull-out strength of sutures and anchors. Peak moment for a large 3 cm gap length was 5.09 Nm, a 53% reduction in moment-generating capacity compared to uninjured supraspinatus.

Interpretation

We conclude that shoulder posture is an important determinant of passive forces during rotator cuff repair surgery. Choosing postures that reduce forces intraoperatively to permit repair of larger gaps may lead to failure postoperatively when the shoulder is mobilized. For larger defects, loss of strength in supraspinatus may be substantial following repair even if retear is prevented.     

Effects of continuous haemofiltration on serum enzyme concentrations, endotoxemia, homeostasis and survival in dogs with severe heat stroke

Aim

To examine the effectiveness of continuous haemofiltration as a treatment for severe heat stroke in dogs.

Methods

Dogs were randomly allocated to a control or continuous haemofiltration group (both n = 8). Heat stroke was induced by placing anaesthetised dogs in a high temperature cabin simulator. Upon confirmation of heat stroke (rectal temperature > 42 °C, mean arterial pressure (MAP) decrease > 25 mmHg), dogs were removed from the chamber and continuous haemofiltration was initiated and continued for 3 h for dogs in the continuous haemofiltration group. Dogs in the control group were observed at room temperature.

Results

Rectal temperature, haemodynamics, pH, blood gases and electrolyte concentrations rapidly returned to baseline in the continuous haemofiltration group, but not the control group. After 3 h, rectal temperature was 36.68 ± 0.51 °C in the continuous haemofiltration group and 39.83 ± 1.10 °C in the control group (P < 0.05). Continuous haemofiltration prevented endotoxin and all serum enzyme concentrations from increasing and caused malondialdehyde concentrations to decrease. After 3 h, endotoxin concentrations were 0.14 ± 0.02 EU ml⁻¹ in the continuous haemofiltration group and 0.23 ± 0.05 EU ml⁻¹ in the control group (P = 0.003), while malondialdehyde concentrations were 4.86 ± 0.61 mmol l⁻¹ in the continuous haemofiltration group and 8.63 ± 0.66 mmol l⁻¹ in the control group (P < 0.001). Five dogs died in the control group within 3 h, whereas no dogs died in the continuous haemofiltration group.

Conclusions

Continuous haemofiltration rapidly reduced body temperature, normalised haemodynamics and electrolytes, improved serum enzyme concentrations and increased survival in dogs with heat stroke. Continuous haemofiltration may be an effective treatment for heat stroke.     

Effects on tibiofemoral biomechanics from kneeling

Background

Repetitive kneeling in certain occupations, hobbies and cultures is associated with tibiofemoral joint osteoarthritis. The biomechanics of kneeling is therefore of interest. This cadaveric study investigated tibiofemoral joint contact areas, pressures, and kinematics in response to kneeling.

Methods

Five human cadaveric knees were subjected to simulated kneeling at flexion angles of 90°, 105°, 120°, and 135°. Different anterior forces were applied to the knee to simulate crouching (no force), double stance kneeling (339 N of force), and single stance kneeling (678 N of force). Tibiofemoral joint kinematics, contact areas, and pressures were measured.

Findings

Kneeling produced tibial posterior translation and external rotation. Posterior translation was significantly less at 90° than at higher flexion angles (P < 0.05). Posterior translation and external rotation were significantly greater moving from crouching to double stance kneeling when compared to moving from double to single stance kneeling (P < 0.05). Double and single stance kneeling increased contact areas and pressures significantly when compared to crouching (P < 0.05). Pressures also increased significantly moving from double to single stance kneeling (P < 0.05).

Interpretation

Kneeling produces less tibial posterior translation at 90° than at higher flexion angles primarily due to posterior cruciate ligament biomechanics. Tibial external rotation results from posterior cruciate ligament biomechanics and differences between medial and lateral compartment anatomy. Different anatomical constraints allow significantly less posterior translation and external rotation moving from double to single stance kneeling is a result of increased pressure with kneeling likely contributes to the development of tibiofemoral osteoarthritis, and single stance kneeling may be more deleterious than double stance kneeling.     

Body temperature regulation and outcome after cardiac arrest and therapeutic hypothermia

Objective

Therapeutic temperature modulation is recommended after cardiac arrest (CA). However, body temperature (BT) regulation has not been extensively studied in this setting. We investigated BT variation in CA patients treated with therapeutic hypothermia (TH) and analyzed its impact on outcome.

Methods

A prospective cohort of comatose CA patients treated with TH (32–34 °C, 24 h) at the medical/surgical intensive care unit of the Lausanne University Hospital was studied. Spontaneous BT was recorded on hospital admission. The following variables were measured during and after TH: time to target temperature (TTT = time from hospital admission to induced BT target <34 °C), cooling rate (spontaneous BT − induced BT target/TTT) and time of passive rewarming to normothermia. Associations of spontaneous and induced BT with in-hospital mortality were examined.

Results

A total of 177 patients (median age 61 years; median time to ROSC 25 min) were studied. Non-survivors (N = 90, 51%) had lower spontaneous admission BT than survivors (median 34.5 [interquartile range 33.7–35.9] °C vs. 35.1 [34.4–35.8] °C, p = 0.04). Accordingly, time to target temperature was shorter among non-survivors (200 [25–363] min vs. 270 [158–375] min, p = 0.03); however, when adjusting for admission BT, cooling rates were comparable between the two outcome groups (0.4 [0.2–0.5] °C/h vs. 0.3 [0.2–0.4] °C/h, p = 0.65). Longer duration of passive rewarming (600 [464–744] min vs. 479 [360–600] min, p < 0.001) was associated with mortality.

Conclusions

Lower spontaneous admission BT and longer time of passive rewarming were associated with in-hospital mortality after CA and TH. Impaired thermoregulation may be an important physiologic determinant of post-resuscitation disease and CA prognosis. When assessing the benefit of early cooling on outcome, future trials should adjust for patient admission temperature and use the cooling rate rather than the time to target temperature.     

Impact of ankle osteoarthritis on the energetics and mechanics of gait: the case of hemophilic arthropathy

Background

Osteoarthritis may affect joints in any part of the body, including the ankle. The purpose of this study was to assess the impact of ankle osteoarthritis on the energetics and mechanics of gait, while taking into account the effect of slower speed generally adopted by patients with osteoarthritis.

Methods

Using a motion analysis system, synchronous kinematic, kinetics, spatiotemporal, mechanics and metabolic gait parameters were measured in 10 patients diagnosed with ankle osteoarthritis consecutive to hemophilia. The subjects walked at a self-selected speed and their performance was compared to speed-matched normal values obtained in healthy control subjects.

Findings

Speed-normalization using a Z-score transformation showed a significant increase in metabolic cost (Z = 1.78; P = 0.006) and decrease in mechanical work (Z = − 0.97; P = 0.009). As a consequence, muscular efficiency also decreased (Z = − 0.97; P = 0.001). These changes were associated with a surprising efficacy of the pendular mechanism, i.e., an improved recovery index (Z = 0.97; P = 0.004).

Interpretation

Our findings suggest that patients with ankle osteoarthritis adopt a walking strategy which improves recovery through the pendular mechanism. This may be a compensatory mechanism in order to economize energy which would counterbalance the energy waste due to low muscle efficiency. These modifications are proportional to the impaired ankle function. Our data provides a quantitative baseline to better understand the dynamics of ankle osteoarthritis and determine the individual role that lower limb joints play in the multiple chronic joint affections.     

The specificity of fatiguing protocols affects scapular orientation: Implications for subacromial impingement

Background

Shoulder impairments are often associated with altered scapular kinematics. As muscles control scapular movement, functionally altering muscle performance through fatigue may produce scapular kinematics that mimic those of injured patients. The aim of this study was to examine if changes in scapular tilt, rotation and pro/retraction following two different upper extremity fatiguing protocols have any implications with respect to subacromial impingement.

Methods

Scapular orientation was monitored during posturally constrained static holds (at 0°, 45° and 90° of humeral elevation) before and after two fatiguing protocols, one global and one local. Both protocols are associated with producing changes in shoulder skeletal arrangement.

Findings

Following the global fatiguing protocol, there was significantly more scapular posterior tilt (P < 0.01) and upward rotation (P < 0.02), particularly at 90° humeral elevation. No changes in scapular orientation occurred following the local fatiguing protocol.

Interpretation

Scapular orientation changes following muscle fatigue acted to increase the subacromial space. Thus, the rotator cuff muscles, not the scapular stabilizers, have more influence on actively preventing mechanical subacromial impingement. The lack of evidence of reduction of the subacromial space thus implicates superior humeral head translation as a more likely primary mechanism of the initiation of subacromial impingement.     

Whole body, long-axis rotational training improves lower extremity neuromuscular control during single leg lateral drop landing and stabilization

Background

Poor neuromuscular control during sports activities is associated with non-contact lower extremity injuries. This study evaluated the efficacy of progressive resistance, whole body, long-axis rotational training to improve lower extremity neuromuscular control during a single leg lateral drop landing and stabilization.

Methods

Thirty-six healthy subjects were randomly assigned to either Training or Control groups. Electromyographic, ground reaction force, and kinematic data were collected from three pre-test, post-test trials. Independent sample t-tests with Bonferroni corrections for multiple comparisons were used to compare group mean change differences (P ≤ 0.05/21 ≤ 0.0023).

Findings

Training group gluteus maximus and gluteus medius neuromuscular efficiency improved 35.7% and 31.7%, respectively. Training group composite vertical–anteroposterior–mediolateral ground reaction force stabilization timing occurred 1.35 s earlier. Training group knee flexion angle at landing increased by 3.5°. Training group time period between the initial two peak frontal plane knee displacements following landing increased by 0.17 s. Training group peak hip and knee flexion velocity were 21.2°/s and 20.1°/s slower, respectively. Time period between the initial two peak frontal plane knee displacements following landing and peak hip flexion velocity mean change differences displayed a strong relationship in the Training group (r² = 0.77, P = 0.0001) suggesting improved dynamic frontal plane knee control as peak hip flexion velocity decreased.

Interpretation

This study identified electromyographic, kinematic, and ground reaction force evidence that device training improved lower extremity neuromuscular control during single leg lateral drop landing and stabilization. Further studies with other populations are indicated.     

The impact of capitellar arthroplasty on elbow contact mechanics: Implications for implant design

Background

Radiocapitellar arthroplasty is indicated for capitellar deficiency. Although current implants employ a spherical capitellar surface, the capitellum is elliptical. This has implications for congruency and wear in capitellar arthroplasty. Our objective was to evaluate the contact mechanics of radiocapitellar arthroplasty. We hypothesized that capitellar replacement would decrease joint contact area relative to the native articulation; and an anatomical implant design would replicate more normal contact morphology than a spherical implant.

Methods

Eight paired humeri and radii were potted in a custom jig. A compressive load of 85 N was applied with the articulation flexed at 45° in neutral forearm rotation. Joint casts were made and the articular contact area and shape were quantified. Anatomical and spherical capitellar implants were tested against the native radial head (hemiarthroplasty).

Findings

The contact areas for the anatomical and spherical hemiarthroplasties were 59 and 51% of the native articulation (P < 0.005), while the unicompartmental arthroplasties' contact areas were 84 and 89% (anatomical, spherical) of the native articulation (P < 0.01). No implant was superior in recreating the native contact shape.

Interpretation

Placement of any capitellar implant resulted in a large decrease in contact area when articulating with a native radial head. This suggests that the radial head cartilage would see a marked increase in contact pressure relative to the native articulation. The unicompartmental arthroplasties demonstrated an even larger reduction in contact area, raising concern about accelerated surface wear. Further investigation needs to correlate these contact mechanics to cartilage wear and implant longevity.     

Alterations in in vivo knee joint kinematics following a femoral nerve branch block of the vastus medialis: Implications for patellofemoral pain syndrome

Background

A potential source of patellofemoral pain, one of the most common problems of the knee, is believed to be altered patellofemoral kinematics due to a force imbalance around the knee. Although no definitive etiology for this imbalance has been found, a weak vastus medialis is considered a primary factor. Therefore, this study's purpose was to determine how the loss of vastus medialis obliquus force alters three-dimensional in vivo knee joint kinematics during a volitional extension task.

Methods

Eighteen asymptomatic female subjects with no history of knee pain or pathology participated in this IRB approved study. Patellofemoral and tibiofemoral kinematics were derived from velocity data acquired using dynamic cine-phase contrast MRI. The same kinematics were then acquired immediately after administering a motor branch block to the vastus medialis obliquus using 3–5 ml of 1% lidocaine. A repeated measures analysis of variance was used to test the null hypothesis that the post- and pre-injection kinematics were no different.

Findings

The null hypothesis was rejected for patellofemoral lateral shift (P = 0.003, max change = 1.8 mm, standard deviation = 1.7 mm), tibiofemoral lateral shift (P < 0.001, max change = 2.1 mm, standard deviation = 2.9 mm), and tibiofemoral external rotation (P < 0.001, max change = 3.7°, standard deviation = 4.4°).

Interpretation

The loss of vastus medialis obliquus function produced kinematic changes that mirrored the axial plane kinematics seen in individuals with patellofemoral pain, but could not account for the full extent of these changes. Thus, vastus medialis weakness is likely a major factor in, but not the sole source of, altered patellofemoral kinematics in such individuals.     

Biomechanical evaluation of two intramedullary nailing techniques with different locking options in a three-part fracture proximal humerus model

Background

Osteosynthesis of unstable proximal humerus fractures still remains challenging. The aim of this study was to investigate two intramedullary nailing techniques with different locking options in a three-part fracture model and prove whether two new fixation concepts, introducing additional locking screw-in-screws inserted through the head of the proximal screws, and a calcar screw, provide better stability.

Methods

A biomechanical testing model for three-part proximal humerus fractures including cyclic axial loading with increasing peak load and simultaneous pulling forces at the rotator cuff was used to test 12 pairs of human cadaver humeri, assigned to four groups and instrumented with either Targon PH (T1) or MultiLoc PHN in 3 different configurations (standard M1; two additional screw-in-screw M2; one additional calcar screw and two screw-in-screw M3).

Findings

Initial range of motion in internal–external rotation and mediolateral translation was smallest in M3 (1.82°; 0.11 mm), biggest in T1 (3.63°; 0.51 mm) and significantly different between these two groups (p = 0.02 and p = 0.04, respectively). M3 showed minimum head migration along the nail and varus tilting after 5000 cycles (0.31 mm; 0.20°) and 10000 cycles (1.59 mm; 0.34°). M2 and M3 performed better than M1 and T1 regarding varus collapse. The highest number of cycles to failure was observed for M3 (20733) and the lowest for T1 (10083) with significant difference between these two groups (p = 0.04).

Interpretation

The configuration with two screw-in-screw and a calcar screw was superior in most aspects. The screw-in-screws were found to contribute against varus collapse. Both new fixation concepts could provide better stability in proximal humerus fractures.     

Greater Q angle may not be a risk factor of patellofemoral pain syndrome

Background

A greater Q-angle has been suggested as a risk factor for Patellofemoral Pain Syndrome. Greater frontal plane knee moment and impulse have been found to play a functional role in the onset of Patellofemoral Pain Syndrome in a running population. Therefore, the purpose of this investigation was to determine the relationship between Q-angle and the magnitude of knee abduction moment and impulse during running.

Methods

Q-angle was statically measured, using a goniometer from three markers on the anterior superior iliac spine, the midpoint of the patella and the tibial tuberosity. Thirty-one recreational runners (21 males and 10 females) performed 8–10 trials running at 4 m/s (SD 0.2) on a 30 m-runway. Absolute and normalized knee moment and impulse were calculated and correlated with Q-angle.

Findings

Negative correlations between Q-angle and the magnitude of peak knee abduction moment (R² = 0.2444, R = − 0.4944, P = 0.005) and impulse (R² = 0.2563, R = − 0.5063, P = 0.004) were found. Additionally, negative correlations between Q-angle and the magnitude of weight normalized knee abduction moment (R² = 0.1842, R = − 0.4292, P = 0.016) and impulse (R² = 0.2304, R = − 0.4801, P = 0.006) were found.

Interpretation

The findings indicate that greater Q-angle, which is actually associated with decreased frontal plane knee abduction moment and impulse during running, may not be a risk factor of Patellofemoral Pain Syndrome.     

Hamstrings loading contributes to lateral patellofemoral malalignment and elevated cartilage pressures: an in vitro study

Background

Hamstrings loading has previously been shown to increase tibiofemoral posterior translation and external rotation, which could contribute to patellofemoral malalignment and elevated patellofemoral pressures. The current study characterizes the influence of forces applied by the hamstrings on patellofemoral kinematics and the pressure applied to patellofemoral cartilage.

Methods

Ten knees were positioned at 40°, 60° and 80° of flexion in vitro, and loaded with 586 N applied through the quadriceps, with and without an additional 200 N applied through the hamstrings. Patellofemoral kinematics were characterized with magnetic sensors fixed to the patella and the femur, while the pressure applied to lateral and medial patellofemoral cartilage was measured with pressure sensors. A repeated measures ANOVA with three levels, combined with paired t-tests at each flexion angle, determined if loading the hamstrings significantly (P < 0.05) influenced the output.

Findings

Loading the hamstrings increased the average patellar flexion, lateral tilt and lateral shift by approximately 1°, 0.5° and 0.2 mm, respectively. Each increase was significant for at least two flexion angles. Loading the hamstrings increased the percentage of the total contact force applied to lateral cartilage by approximately 5%, which was significant at each flexion angle, and the maximum lateral pressure by approximately 0.3 MPa, which was significant at 40° and 60°.

Interpretation

The increased lateral shift and tilt of the patella caused by loading the hamstrings can contribute to lateral malalignment and shifts pressure toward the lateral facet of the patella, which could contribute to overloading of lateral cartilage.     

Changes in patellofemoral joint contact pressures caused by vastus medialis muscle weakness

Background

Patellofemoral joint pain is a common knee disorder, but its underlying causes remain unknown. One proposed mechanism is an imbalance in force in the knee extensor muscles. Specifically, the vastus medialis and vastus lateralis are thought to play a crucial role in proper patellar tracking, and weakness in vastus medialis is thought to lead to a lateral shift in the patella causing increased contact pressures and pain. The purpose of this study was to create an animal model of vastus medialis weakness and to test the effect of this weakness on patellofemoral contact pressures.

Methods

Experiments were performed using New Zealand white rabbits (mass 4.9–7.7 kg, n = 12). Loading of the patellofemoral joint was produced by femoral nerve stimulation of the knee extensor muscles. Knee extensor imbalance was produced by vastus medialis ablation. Fuji pressure sensitive film was used to record contact area, shape and pressures for maximal and sub-maximal, matched-force contractions at knee angles of 30°, 60°, and 90°.

Findings

Patellofemoral peak pressures, average pressures, contact areas and contact shapes were the same across all loading conditions for matched-force contractions before and after elimination of vastus medialis.

Interpretation

We conclude that vastus medialis weakness does not cause changes in patellofemoral contact pressures. Since the muscular and knee joint geometry in rabbits and humans is similar, we question the idea of vastus medialis weakness as a cause of patellar mal-tracking and patellofemoral joint pain.     

Breath analyzer screening of emergency department patients suspected of alcohol intoxication

Background

Acute alcohol intoxication is a frequent cause of emergency department (ED) visits. Evaluating a patient’s alcohol intoxication is commonly based on both a physical examination and determination of blood alcohol concentration (BAC).

Objective

To demonstrate the feasibility and usefulness of using a last-generation infrared breath analyzer as a non-invasive and rapid screening tool for alcohol intoxication in the ED.

Methods

Adult patients suspected of acute alcohol intoxication were prospectively enrolled over 10 days. Breath alcohol concentrations (BrAC) were measured using a handheld infrared breath analyzer. BAC was determined simultaneously by automated enzymatic analysis of a venous blood sample. The relationship between BAC and BrAC values was examined by both linear regression and Bland-Altman analysis.

Results

The study included 54 patients (mean age 40 ± 14 years, sex ratio M/F of 3/1). Breath and blood alcohol concentrations ranged from 0 to 1.44 mg/L and from 0 to 4.40 g/L (0–440 mg/dL), respectively. The mean individual BAC/BrAC ratio was 2615 ± 387, 95% confidence interval 2509–2714, which is 30% higher than the legal ratio in France (2000). The correlation between both measurements was excellent: r = 0.95 (0.92–0.97). Linear regression revealed BAC = 0.026 + 1.29 (BrAC × 2000) and BAC = 0.026 + 0.99 (BrAC × 2615). Mean BAC-BrAC differences and limits of agreement were 0.49 g/L [−0.35, 1.34] (or 49 mg/dL [−35, 134] and 0.01 g/L [−0.68, 0.71] (or 1 mg/dL [−68, 71]), for the 2000 and 2615 ratios, respectively.

Conclusion

The calculated conversion coefficient provided a satisfactory determination of blood alcohol concentration. Breath alcohol testing, using appropriate BAC/BrAC conversion, different from the legal BAC/BrAC, could be a reliable alternative for routine screening and management of alcohol intoxication in the ED.     

Role of cardiac troponin in the diagnosis of acute myocardial infarction in comatose patients resuscitated from out-of-hospital cardiac arrest

Background

Troponin is a major diagnostic criterion of acute myocardial infarction (AMI) but in out-of-hospital cardiac arrest (OHCA) patients, its diagnostic value may be altered by cardiopulmonary resuscitation.

Methods

Single-centre study assessing the diagnostic characteristics of troponin for AMI diagnosis in consecutive patients resuscitated from OHCA between 2002 and 2008 with coronary angiogram (CA) performed on admission. Patients with obvious non-cardiac cause of OHCA, unsustained or absent return of spontaneous circulation were excluded. AMI was defined on CA by the presence of acute occlusion or critical stenosis with intracoronary fresh thrombus easily crossed by an angioplasty wire. Troponin concentration was recorded once on admission and once 6–12 h after the OHCA.

Results

A total of 163 patients aged 56 (median) years (interquartile range (IQR) 48–65) was included, all comatose. Most prevalent initial OHCA rhythms were ventricular fibrillation (49%) and asystole (41%). AMI was diagnosed on coronary angiogram in 37% of the patients.Median troponin concentration on admission was 1.7 (0.3–10) ng ml⁻¹ and sensitivity for AMI diagnosis was 72% and specificity 75% for a 2.5 ng ml⁻¹ cut-off. A combined criterion comprising ST elevation and troponin >2.5 ng ml⁻¹ had a sensitivity of 93% and specificity of 64%.Six to twelve hours after the OHCA, median troponin concentration was 7.6 ng ml⁻¹ (1.4–47.5), sensitivity was 84% and specificity 84% for a 14.5 ng ml⁻¹ cut-off.

Conclusion

Troponin I has a good diagnostic value for AMI diagnosis in OHCA patients. In combination with ST elevation, troponin I on admission achieves a very high sensitivity.