Biomechanical evaluation of different abduction splints for the treatment of congenital hip dysplasia

Background

Abduction splints for the treatment of hip dysplasia normally operate on curbing the legs at the hip flexion and abduction. The forces are absorbed in different designs of shoulder straps and thus diverted to the shoulder and the spine. The present study is the first comparing these undesired forces of two spread orthoses and subsequently the transmitted forces to the infant's spine.

Methods

Between March 2009 and October 2009 the hips of 290 infants were investigated by ultrasound within the first 3 days after birth. Thereof 20 infants with a hip dysplasia Graf type IIc, D or IIIa met our inclusion criteria and were investigated with a Tübinger and a Superior abduction splint. Biomechanical evaluation was performed by using a high-sensitive strain gauge sensor applied to the infant's orthoses between pelvic harness and shoulder straps.

Findings

The transmitted forces to the infant's shoulders correlated significantly with their body mass (P < 0.05). Maximal forces on the shoulder of the infants and subsequently transmitted forces on the spine were significantly higher (P < 0.05) with the Tübinger splint (range 7.6 N to 32.3 N; arithmetic mean M: 13.7 N) in comparison to the Superior orthosis (range 0.0 N to 3.5 N; M: 0.7 N).

Interpretation

The Superior orthosis works with primary load transmission to the pelvic bone. Using the Tübinger splint the shoulders of the newborn infants are loaded with a maximum of 93.9% of their body mass. This may influence the development of the growing infant's spine.     

Ageing modifies the fibre angle and biomechanical function of the lumbar extensor muscles

Background

Ageing is associated with geometrical changes in muscle fascicles that may lead to deteriorations in physical functions. The purpose of this study was to study the effects of ageing on fibre orientation and strength of the lumbar extensor muscles.

Methods

Fifty two healthy, 26 younger (10 males and 16 females, aged from 20 to 35) and 26 older (10 males and 16 females, aged from 65 to 90) volunteers participated in this study. Ultrasound images of the lumbar extensor muscles were obtained with the participants in relaxed standing and half flexion (50% of the range of trunk flexion). The fibre angles at the mid-substance of the muscle were recorded. Lumbar extensor muscle strength was measured in the upright posture with a load cell.

Findings

The mean lumbar extensor fibre angles were found to significantly decrease in the half flexion posture when compared to upright stance (P < 0.01). Both the fibre angle and the moment generation capability of the muscles decreased with ageing (P < 0.01). There was a moderate correlation between the fibre angles in the upright posture and the muscle strength measured in this posture (r = 0.40, P < 0.01).

Interpretation

Age-related changes in muscle geometry and posture may partly account for the deterioration in muscle function in the elderly.     

Influence of cementing the pin on resistance to fracture in hip resurfacing

Background

Since the introduction of modern hip resurfacing systems, there has been a controversy regarding the fixation of the centering pin in the femoral component. It has been suggested that cementing the pin may increase strength of the femoral neck. This in-vitro analysis investigated the influence of a cemented, femoral pin on resistance to fracture in the resurfaced hip.

Methods

Five pairs of cadaveric, fresh-frozen femora underwent hip resurfacing (ASR™) using a high viscosity cementing technique. In one side of each pair only the inner surface of the implant was cemented, in the other side, cement was additionally hand-pressurized down the pinhole prior to implantation of the femoral component. Specimen were then mounted on a material testing machine and cyclic loading with increasing load steps was applied until fracture of the femoral neck.

Findings

Fracture load was increased (P = 0.013) in the cemented pin group (Median = 4200 N) when compared with the cementless pin group (Median = 2800 N). The number of cycles to failure in the group with the cemented pin (Median = 8072) was likewise higher (P = 0.01) when compared to the group, in which the pin was not cemented (Median = 5906).

Interpretation

Cementing the pin may provide additional fixation in hips with low bone mineral density or osteonecrotic lesions, as resistance to fracture could be improved in the presented in-vitro scenario. Although this was shown for a specific hip resurfacing system, this effect might be extrapolated to other, similar implant designs.     

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.     

The effects of spinal posture and pelvic fixation on trunk rotation range of motion

Background

Axial rotation of the trunk is important to many vocational tasks and activities of daily living, and may be associated with back injuries. The influence of spinal postures on trunk rotation appears conflicting. This study investigated the influence of forward trunk inclination, spinal posture and pelvic fixation on maximum trunk rotation.

Methods

Twenty male participants were assessed using an optoelectronic motion-analysis system to track trunk movement during maximal trunk rotations in different spinal positions within the sagittal plane. A repeated-measures multivariate analysis of variance investigated the effects of forward trunk inclination, spinal posture and pelvic fixation on trunk and pelvic rotation. Test–retest reliability was determined using interclass correlation coefficients and standard error of measurement.

Findings

Forward trunk inclination at 45° yielded a 19% (6.2°; P < 0.001) increase in trunk rotation and a 40% (25.5°; P < 0.001) decrease in pelvic rotation when compared to standing. When flexing and extending the spine at a forward trunk inclination of 45° there was a 5% (1.9°; P < 0.01) and a 4% (1.6°; P < 0.05) decrease in trunk rotation. Fixing the pelvis increased the trunk rotation by up to 9% (3.3°; P < 0.001).

Interpretation

Inclining the trunk forward and maintaining a neutral spine maximised trunk rotation range of motion (RoM). This has implications for educational programmes intended to maximise sporting performance. Within the clinical setting, unrestricted observation of trunk rotations is considered more appropriate as it may benefit the clinician in determining possible detrimental relative flexibilities that may exist within the body.     

The relationship between rearfoot, tibial and hip kinematics in individuals with patellofemoral pain syndrome

Background

Excessive rearfoot eversion is thought to be a risk factor for patellofemoral pain syndrome development, based on theoretical rationale linking it to greater tibial internal rotation and hip adduction. This study aimed to establish the relationship of rearfoot eversion with tibial internal rotation and hip adduction during walking in individuals with and without patellofemoral pain syndrome.

Methods

Twenty-six individuals with patellofemoral pain syndrome and 20 controls (18–35 years) participated. Each underwent instrumented three-dimensional motion analysis during over-ground walking. Pearson's correlation coefficients (r) were calculated to establish the relationship of rearfoot eversion with tibial internal rotation and hip adduction (peak and range of motion).

Findings

Greater peak rearfoot eversion was associated with greater peak tibial internal rotation in the patellofemoral pain syndrome group (r = 0.394, P = 0.046). Greater rearfoot eversion range of motion was associated with greater hip adduction range of motion in the patellofemoral pain syndrome (r = 0.573, P = 0.002) and control (r = 0.460, P = 0.041) groups; and greater peak hip adduction in the control group (r = 0.477, P = 0.033).

Interpretation

Associations between greater rearfoot eversion and greater hip adduction indicate that interventions targeted at the foot or hip in individuals with patellofemoral pain syndrome may have similar overall effects on lower limb motion and clinical outcomes. The relationship between rearfoot eversion and tibial internal rotation identified in the patellofemoral pain syndrome group may be related to aetiology. However, additional prospective research is needed to confirm this.     

Lower limb muscle strengthening does not change frontal plane moments in women with knee osteoarthritis: A randomized controlled trial

Background

Osteoarthritis is a common musculo-skeletal problem accompanied with muscle weakness. Muscle weakness may be readily improved by resistance training. Greater muscle strength has been associated with a lower knee joint loading rate.

Methods

We conducted a single-blind randomized controlled trial of 54 female patients with osteoarthritis in at least one knee, according to the American College of Rheumatology clinical criteria. Patients were randomized into a 6-month high intensity progressive resistance training or a sham-exercise program. The primary outcomes were first peak knee and hip adduction moment measured using three-dimensional gait analysis at self-selected habitual and maximal speeds. Secondary outcomes were sagittal plane knee and hip moments, peak muscle strength, gait speed, and self-reported knee osteoarthritis symptoms measured by the Western Ontario and McMaster Osteoarthritis Index (WOMAC).

Findings

Six months of high intensity resistance training did not change the first peak knee or hip adduction moment at either habitual or maximum walking speeds (P > 0.413) compared to the sham-exercise. However, the second peak hip adduction moment (P = 0.025) and WOMAC pain score (P < 0.001) were reduced significantly in both groups over time, but there was no group effect. The changes in the second peak hip adduction moment were inversely related to the changes in the WOMAC pain score (r = − 0.394, P = 0.009).

Interpretations

Muscle strength training in women with osteoarthritis, while effective for reducing osteoarthritis symptoms, appeared to operate through mechanisms other than improved knee or hip joint loading, as paradoxically, improved symptoms were related to decreases of hip adduction moment in late stance.     

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.     

In vitro quantitative assessment of total and bipolar shoulder arthroplasties: A biomechanical study using human cadaver shoulders

Background

Glenohumeral arthroplasty has produced results far inferior to those seen with hip and knee joint procedures. Therefore, the objective of this study was to evaluate the biomechanical parameters of the glenohumeral joint before and after total shoulder arthroplasty and bipolar hemiarthroplasty in 12 different positions simulating overhead activities.

Methods

Six matched pairs of cadaveric shoulders were used with a custom shoulder testing system to quantify the joint reactive force, contact areas, contact patterns and contact pressures in 12 different positions simulating overhead activities. The entire study was performed for the anatomic glenohumeral joint and following total shoulder arthroplasty on one side, and for the anatomic glenohumeral joint and following bipolar shoulder hemiarthroplasty on the contra-lateral side.

Findings

There was a significant increase in posterior force following total shoulder arthroplasty in two positions of horizontal adduction (P < 0.05). In positions of increased glenohumeral abduction and horizontal adduction, the contact pressures and patterns were greatly altered following both total shoulder arthroplasty and bipolar hemiarthroplasty procedures compared to the anatomic state.

Interpretation

The alterations in joint reaction force, contact pressure and contact patterns following shoulder arthroplasty suggest a possible etiology for glenoid component edge loading in patients following total shoulder arthroplasty. This edge loading may lead to a rocking phenomenon of the glenoid component and subsequent loosening.     

Differences in posture-movement changes induced by repetitive arm motion in healthy and shoulder-injured individuals

Background

Neck/Shoulder pain is linked to movement repetition, awkward postures, prolonged maintenance of static postures, and muscular fatigue. Studies have examined the influence of pain and fatigue on movement characteristics, but few reported multi-dimensional adaptations to movement repetition. We compared the adaptations measured in three-dimensions during a repetitive reaching task in persons with chronic neck/shoulder pain and healthy subjects.

Methods

A shoulder-injured group (intensity > 3/10, duration > 3 consecutive months) and an age–sex-matched control group (n = 16 in each) performed a repetitive reaching task to voluntary termination. Kinematics, kinetics, heart rate and muscle activity were recorded throughout. Power output on a 10-s pushing/pulling task was assessed pre- and post-reaching. Group comparisons were made in absolute time and at task end.

Findings

Control subjects performed the task 55% longer than the pain group; yet, both groups demonstrated task-related increased heart rate (6 beats per minute) and decreased power output (6 W). Throughout the task, the pain group demonstrated: higher supraspinatus activity, and less elbow flexion and endpoint movement. The control group increased movement amplitude of the endpoint, elbow, and shoulder, while the pain group moved the shoulder less and increased center of mass excursion to maintain the task.

Interpretation

Both groups adapted to the task in unique ways. The control group continually increased elbow and endpoint range of motion, bringing the arm closer to the targets, possibly to prolong task performance. The pain group used a fixed, en block arm strategy, likely to reduce the load on the injured structures; however, this may place other structures at risk for pain and injury.     

Effects of unloading bracing on knee and hip joints for patients with medial compartment knee osteoarthritis

Background

Osteoarthritis affects the whole body, thus biomechanical effects on other joints should be considered. Unloading knee braces could be effective for knee osteoarthritis, but their effects on the contralateral knee and bilateral hip joints remain unknown. This study investigated the effects of bracing on the kinematics and kinetics of involved and contralateral joints during gait.

Methods

Nineteen patients with medial compartment knee osteoarthritis were analysed. Kinematics and kinetics of the knee and hip joints in frontal and sagittal planes were measured during walking without and with bracing on the more symptomatic knee.

Findings

The ipsilateral hip in the braced condition showed a lower adduction angle by an average of 2.58° (range, 1.05°–4.16°) during 1%–49% of the stance phase, and a lower abduction moment at the second peak during the stance phase than the hip in the unbraced condition (P < 0.05 and P < 0.005, respectively). With bracing, the contralateral hip showed a more marked peak extension moment and lower abduction moment at the first peak (P < 0.05), and the contralateral knee adduction angle increased by an average of 0.32° (range, 0.21°–0.45°) during 46%–55% of the stance phase (P < 0.05), compared to no bracing.

Interpretation

Unloading bracing modified the contralateral knee adduction angle pattern at a specific time point during gait. It also affected the frontal plane on the ipsilateral hip and the frontal and sagittal planes on the contralateral hip joint. Consideration should be provided to other joints when treating knee osteoarthritis.     

Age-related changes in speed and accuracy during rapid targeted center of pressure movements near the posterior limit of the base of support

Background

Backward falls are often associated with injury, particularly among older women. An age-related increase occurs in center of pressure variability when standing and leaning. So, we hypothesized that, in comparison to young women, older women would display a disproportionate decrease of speed and accuracy in the primary center of pressure submovements as movement amplitude increases.

Methods

Ground reaction forces were recorded from thirteen healthy young and twelve older women while performing rapid, targeted, center of pressure movements of small and large amplitude in upright stance. Measures included center of pressure speed, the number of center of pressure submovements, and the incidence rate of primary center of pressure submovements undershooting the target.

Findings

In comparison to young women, older women used slower primary submovements, particularly as movement amplitude increased (P < 0.01). Even though older women achieved similar endpoint accuracy, they demonstrated a 2 to 5-fold increase in the incidence of primary submovement undershooting for large-amplitude movements (P < 0.01). Overall, posterior center of pressure movements of older women were 41% slower and exhibited 43% more secondary submovements than in young women (P < 0.01).

Interpretations

We conclude that the increased primary submovement undershoots and secondary center of pressure submovements in the older women reflect the use of a conservative control strategy near the posterior limit of their base of support.     

Low back pain status affects pelvis-trunk coordination and variability during walking and running

Background

The purpose of this study was to compare pelvis–trunk coordination and coordination variability over a range of walking and running speeds between three groups of runners; runners with low to moderate low back pain; runners who had recovered from a single bout of acute low back pain; and runners who had never experienced any symptoms of low back pain.

Methods

Pelvis and trunk kinematic data were collected as speed was systematically increased on a treadmill. Coordination between pelvis and trunk in all three planes of motion was measured using continuous relative phase, and coordination variability was defined as the standard deviation of this measure.

Findings

Oswestry Disability Index indicated the low back pain group was high functioning (mean 7.9% out of 100%). During walking, frontal plane coordination was more in-phase for the low back pain group compared to controls (P = 0.029), with the resolved group showing an intermediate coordination pattern (P = 0.064). During running, both low back pain (P = 0.021) and resolved (P = 0.025) groups showed more in-phase coordination in the transverse plane than the control group. The low back pain group also showed reduced transverse plane coordination variability compared to controls (P = 0.022).

Interpretation

Coordination and coordination variability results showed a continuum of responses between our three groups. Taken together, the data lend insight into increased injury risk and performance deficits associated with even one bout of low back pain, and suggest that clinicians need to look beyond the resolution of pain when prescribing rehabilitation for low back pain.     

Kinematic and kinetic modifications in walking pattern of hip osteoarthritis patients induced by intra-articular injections of hyaluronic acid

Background

A growing body of evidence points to the efficacy of intra-articular injections of hyaluronic acid, in dealing with pain and function in hip osteoarthritis. To date, however, no data exist as to this treatment's effect on walking pattern.

Methods

We performed a prospective, open study in order to verify, in a group of 20 hip osteoarthritis patients (12 men, 8 women, mean age 60.5, range 47–73), the clinical effects of 3 intra-articular injections of 2 ml of hyaluronic acid in the hip (1/week) in terms of pain and function at 1 (T1), 3 (T2) and 6-month (T3) follow-ups, as well as changes in the kinematics and kinetics of gait at 6-month follow-up.

Findings

Pain as measured with visual analog scale significantly dropped after this procedure (P < 0.0001). A significant improvement was noted regarding stiffness (P = 0.005) and disability (P = 0.04), as measured by the Western Ontario and McMaster Universities osteoarthritis index. As regards gait analysis, patients at T3 walked with higher cadence (P = 0.004) and stride length (P = 0.02) compared to T0. Moreover, a significant increase for the pelvic tilt at heel contact (P = 0.0004) and for hip flexion–extension moment at loading response sub-phases of gait cycle (P = 0.02) was noted at T3.

Interpretation

In line with current literature, our patients display clinical improvement 6 months after intra-articular injections of hyaluronic acid, accompanied by changes in walking pattern, as measured by instrumental gait analysis. The kinematic and kinetic changes observed may be the consequence of the therapeutic effect of intra-articular injections of hyaluronic acid.     

Changes in infraspinatus cross-sectional area and shoulder range of motion with repetitive eccentric external rotator contraction

Background

Repetitive eccentric loading results in muscle damage and subsequent changes in muscle stiffness and edema accumulation, which manifest as reduced joint range of motion and increased muscle cross-sectional area. The purpose of the study was to evaluate changes in shoulder range of motion and the infraspinatus cross-sectional area with repetitive eccentric contraction.

Methods

Twenty physically active participants performed 9 sets of 25 repetitions of eccentric external rotator contractions. The ultrasonographic measurement of the infraspinatus cross-sectional area, and shoulder internal/external rotation and horizontal adduction range of motion were measured before, immediately after, and 24 h after the intervention.

Findings

Infraspinatus cross-sectional area significantly increased from baseline immediately after exercise (P < 0.001), and remained elevated from baseline at the 24-hour follow up (P < 0.001). Internal rotation and horizontal adduction range of motion did not change significantly between baseline and post-exercise (P > 0.05), but were significantly decreased at the 24-hour follow up from the baseline (internal rotation: P < 0.001, horizontal adduction: P < 0.001) and the immediate post-exercise (internal rotation: P = 1.012, horizontal adduction: P = 0.016).

Interpretation

These changes observed after the eccentric contractions may have implications for injury development in pitchers, because 1) the infraspinatus endures repetitive eccentric loading with pitching and 2) decreased internal rotation and horizontal adduction range of motion have been linked to upper extremity injuries. However, since the muscle response after eccentric loading varies by the task and previous exposure to similar stress, future study needs to investigate the time course of recovery of the muscle cross-sectional area and range of motion after pitching in competitive pitchers.     

Range of motion of large head total hip arthroplasty is greater than 28 mm total hip arthroplasty or hip resurfacing

Background

Reduced range of motion of the hip has a detrimental influence on lower limb function. Large diameter head total hip arthroplasty may theoretically have a greater potential for restoring normal hip range of motion due to greater head–neck diameter ratio, and hence provide better function compared to conventional or hip resurfacing arthroplasty.

Method

At minimum one year follow-up, range of motion of the operated and contra lateral hips was clinically assessed using digital photographs and bony landmarks in a clinical comparative study. We assessed if 1) large diameter head total hip arthroplasty (55 patients) restores better hip range of motion compared to 28 mm total hip arthroplasty (50 patients) or hip resurfacing (60 patients) 2) large diameter head total hip arthroplasty achieves same hip range of motion as contra lateral normal hips and 3) hip range of motion correlates with the WOMAC score.

Findings

The large diameter head total hip arthroplasty group had significantly greater total arcs of motion (approximately 20°), mostly due to an increase of hip flexion and external rotation, but did not reach normal hip motion. The hip range of motion showed significant correlation with the WOMAC score, especially the flexion arc.

Interpretation

The better hip range of motion of large diameter head total hip arthroplasty is likely due to the greater head to neck diameter ratio and hence seems to be the best option to optimize range of hip motion and improve function after hip arthroplasty.     

Should extramedullary fixations for hip fractures be removed after bone union?

Background

Osteosynthesis implants, which remain in the patient after fracture union to save additional surgery, may affect the strain distribution within the bone. A reduction of strain within the bone is known to result in localized bone loss (“stress shielding”) and increased fracture risk. The purpose of this study was to examine whether extramedullary fixations for femoral neck fractures have to be removed after fracture union to prevent reductions in cortex strains.

Methods

In a biomechanical experiment, six pairs of human cadaver femora (mean age 56 years, range 48 to 64) were supplied with five strain gauges per bone. The bones were equally supplied with a compression hip screw or a femoral neck plate. Before surgery, after surgery and after removal of the implants, axial compression tests were conducted to measure surface strains during loading.

Findings

The compression hip screw reduced the amount of strain at the superior neck by 88% (P = 0.015) and at the lesser trochanter by 51% (P = 0.038). The femoral neck plate reduced the amount of strain at the superior neck by 89% (P = 0.001), and increased the amount of strain at the inferior neck by 58% (P = 0.02) and at the lesser trochanter by 63% (P = 0.005). After implant removal, there was no significant difference in strain compared to pre-fracture levels, except for the compression hip screw with 21% less strain (P = 0.047) at the superior neck.

Interpretation

Removal of osteosynthesis implants after bone union reverts bone strains to pre-fracture levels, and might prevent further bone loss induced by stress shielding.     

The mechanical effect of the existing cement mantle on the in-cement femoral revision

Background

Cement-in-cement revision hip arthroplasty is an increasingly popular technique to replace a loose femoral stem which retains much of the original cement mantle. However, some concern exists regarding the retention of the existing fatigued and aged cement in such cement-in-cement revisions. This study investigates whether leaving an existing fatigued and aged cement mantle degrades the mechanical performance of a cement-in-cement revision construct.

Methods

Primary cement mantles were formed by cementing a polished stem into sections of tubular steel. If in the test group, the mantle underwent conditioning in saline to simulate ageing and was subject to a fatigue of 1 million cycles. If in the control group no such conditioning or fatigue was carried out. The cement-in-cement procedure was then undertaken. Both groups underwent a fatigue of 1 million cycles subsequent to the revision procedure.

Findings

Application of a Mann–Whitney test on the recorded subsidence (means: 0.51, 0.46, n = 10 + 10, P = 0.496) and inducible displacement (means: 0.38, 0.36, P = 0.96) revealed that there was no statistical difference between the groups.

Interpretation

This study represents further biomechanical investigation of the mechanical behaviour of cement-in-cement revision constructs. Results suggest that pre-revision fatigue and ageing of the cement may not be deleterious to the mechanical performance of the revision construct. Thus, this study provides biomechanical evidence to back-up recent successes with this useful revision technique.     

Reconstruction interlocking nails for ipsilateral femoral neck and shaft fractures: Biomechanical analysis of effect of supplementary cannulated screw on intracapsular femoral neck fracture

Background

To stabilize the femoral head in ipsilateral femoral neck and shaft fractures, one cannulated screw was supplemented in front of the reconstruction interlocking nail (recon nail).

Methods

Twenty-eight left sawbone femurs were divided into two groups. The 14 femurs in each group were osteotomized with subcapital or transcervical fractures. The shafts of all femurs were also osteotomized, and 1 cm of the distal segmental cortex was excised. Next, all the fractures were treated with static recon nails to concomitantly stabilize both femoral neck and shaft fractures. Additionally, seven subcapital fractures and seven transcervical fractures were supplemented with one cannulated screw in front of the recon nails. All specimens were tested with a Material Testing System machine to investigate the relative stability during uniaxial cyclic compression.

Findings

The subcapital and transcervical fractures supplemented with one cannulated screw could bear more loads than those without screw supplementation (P < 0.01 and P < 0.01, respectively at any testing interval). Moreover, in the case of the subcapital fractures, the single supplemented cannulated screw could reduce the displacement at 500 N by 24% (P < 0.001). On the other hand, in the case of the transcervical fractures, one supplemented cannulated screw could reduce the displacement at 500 N by 4% (P = 0.003).

Interpretation

From the biomechanical viewpoint, the subcapital fractures in combined fractures are recommended to supplement with one cannulated screw in front of the recon nails to eliminate complications associated with stabilization.     

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.