Frederick Serra-Hsu

Single-Row Modified Mason-Allen Versus Double-Row Arthroscopic Rotator Cuff Repair : A Biomechanical and Surface Area Comparison

PURPOSE The purpose of this study was to compare the time-zero biomechanical strength and the surface area of repair between a single-row modified Mason-Allen rotator cuff repair and a double-row arthroscopic repair. METHODS Six matched pairs of sheep infraspinatus tendons were repaired by both techniques. Pressure-sensitive film was used to measure the surface area of repair for each configuration. Specimens were biomechanically tested with cyclic loading from 20 N to 30 N for 20 cycles and were loaded to failure at a rate of 1 mm/s. Failure was defined at 5 mm of gap formation. RESULTS Double-row suture anchor fixation restored a mean surface area of 258.23 +/- 69.7 mm(2) versus 148.08 +/- 75.5 mm(2) for single-row fixation, a 74% increase (P = .025). Both repairs had statistically similar time-zero biomechanics. There was no statistical difference in peak-to-peak displacement or elongation during cyclic loading. Single-row fixation showed a higher mean load to failure (110.26 +/- 26.4 N) than double-row fixation (108.93 +/- 21.8 N). This was not statistically significant (P = .932). All specimens failed at the suture-tendon interface. CONCLUSIONS Double-row suture anchor fixation restores a greater percentage of the anatomic footprint when compared with a single-row Mason-Allen technique. The time-zero biomechanical strength was not significantly different between the 2 study groups. This study suggests that the 2 factors are independent of each other. CLINICAL RELEVANCE Surface area and biomechanical strength of fixation are 2 independent factors in the outcome of rotator cuff repair. Maximizing both factors may increase the likelihood of complete tendon-bone healing and ultimately improve clinical outcomes. For smaller tears, a single-row modified Mason-Allen suture technique may provide sufficient strength, but for large amenable tears, a double row can provide both strength and increased surface area for healing.

Dynamic hydraulic fluid stimulation regulated intramedullary pressure.

Physical signals within the bone, i.e. generated from mechanical loading, have the potential to initiate skeletal adaptation. Strong evidence has pointed to bone fluid flow (BFF) as a media between an external load and the bone cells, in which altered velocity and pressure can ultimately initiate the mechanotransduction and the remodeling process within the bone. Load-induced BFF can be altered by factors such as intramedullary pressure (ImP) and/or bone matrix strain, mediating bone adaptation. Previous studies have shown that BFF induced by ImP alone, with minimum bone strain, can initiate bone remodeling. However, identifying induced ImP dynamics and bone strain factor in vivo using a non-invasive method still remains challenging. To apply ImP as a means for alteration of BFF, it was hypothesized that non-invasive dynamic hydraulic stimulation (DHS) can induce local ImP with minimal bone strain to potentially elicit osteogenic adaptive responses via bone-muscle coupling. The goal of this study was to evaluate the immediate effects on local and distant ImP and strain in response to a range of loading frequencies using DHS. Simultaneous femoral and tibial ImP and bone strain values were measured in three 15-month-old female Sprague Dawley rats during DHS loading on the tibia with frequencies of 1Hz to 10Hz. DHS showed noticeable effects on ImP induction in the stimulated tibia in a nonlinear fashion in response to DHS over the range of loading frequencies, where they peaked at 2Hz. DHS at various loading frequencies generated minimal bone strain in the tibiae. Maximal bone strain measured at all loading frequencies was less than 8με. No detectable induction of ImP or bone strain was observed in the femur. This study suggested that oscillatory DHS may regulate the local fluid dynamics with minimal mechanical strain in the bone, which serves critically in bone adaptation. These results clearly implied DHSs potential as an effective, non-invasive intervention for osteopenia and osteoporosis treatments.

Interrelation between external oscillatory muscle coupling amplitude and in vivo intramedullary pressure related bone adaptation

Interstitial bone fluid flow (IBFF) is suggested as a communication medium that bridges external physical signals and internal cellular activities in the bone, which thus regulates bone remodeling. Intramedullary pressure (ImP) is one main regulatory factor of IBFF and bone adaptation related mechanotransduction. Our group has recently observed that dynamic hydraulic stimulation (DHS), as an external oscillatory muscle coupling, was able to induce local ImP with minimal bone strain as well as to mitigate disuse bone loss. The current study aimed to evaluate the dose dependent relationship between DHSs amplitude, i.e., 15 and 30mmHg, and in vivo ImP induction, as well as this correlation on bones phenotypic change. Simultaneous measurements of ImP and DHS cuff pressures were obtained from rats under DHS with various magnitudes and a constant frequency of 2Hz. ImP inductions and cuff pressures upon DHS loading showed a positively proportional response over the amplitude sweep. The relationship between ImP and DHS cuff pressure was evaluated and shown to be proportional, in which ImP was raised with increases of DHS cuff pressure amplitudes (R(2)=0.98). A 4-week in vivo experiment using a rat hindlimb suspension model demonstrated that the mitigation effect of DHS on disuse trabecular bone was highly dose dependent and related to DHSs amplitude, where a higher ImP led to a higher bone volume. This study suggested that sufficient physiological DHS is needed to generate ImP. Oscillatory DHS, potentially induces local fluid flow, has shown dose dependence in attenuation of disuse osteopenia.

Effects of phase cancellation on broadband ultrasonic attenuation for in vitro human trabecular bone using a 2-D synthetic array

The average BV/TV, TB.Th and Tb.Sp for the trabecular bone are 0.154±0.052, 0.203±0.025 mm and 0.812±0.151 mm, respectively. After normalization with sample thickness, the average normalized BUA (nBUA) is 24.8±9.5 dB/MHz/cm and 19.2±5.5 dB/MHz/cm for PS and PI respectively. PS nBUA is significantly different than PI BUA (paired t-test, p<;0.0001). On average, PS nBUA is 28.5% higher than PI BUA, and linear regression shows that PS nBUA can explain 81.2% of the variability in PI nBUA. Both PI nBUA and PS nBUA are highly correlated with BV/TV with coefficients of R=0.911 and R=0.898 (p<;0.0001), respectively. Both PI nBUA and PS nBUA are also highly correlated with Youngs modulus with coefficients of R=0.906 and R=0.822 (p<;0.0001), respectively. Results show that phase cancellation does have a significant effect on BUA. However, both PS nBUA and PI nBUA correlate well with the structural parameter, BV/TV and mechanical strength parameter, Youngs modulus.

Frequency Specific Ultrasound Attenuation Is Sensitive to Trabecular Bone Structure

This study investigated the efficacy of frequency modulated ultrasound attenuation in the assessment of the trabecular structural properties. Four frequency modulated signals were created to represent four frequency bands centered at 500 kHz, 900 kHz, 1.3 MHz and 1.7 MHz with the bandwidth of 400 kHz. Five 1-cm trabecular cubes were harvested from fresh bovine distal femur. The cubes underwent four steps of demineralization process to expand the sample size to 25 with the greater variations of the structural properties for the better correlation study. Pearson correlation study was performed between the ultrasound attenuation in four frequency bands and the trabecular structural properties. The results showed that correlations of frequency modulated ultrasound attenuation to the trabecular structural properties are dependent on frequency bands. The attenuation in proximal-distal orientation had the highest correlation to BV/TV (R(2) = 0.73, p < 0.001) and trabecular thickness (R(2) = 0.50, p < 0.001) at the frequency band centered at 1.7 MHz. It was equivalent in the four frequency bands in correlation to the trabecular number (average R(2) = 0.80, p < 0.001) and to the trabecular separation (average R(2) = 0.83, p < 0.001). The attenuation in anterio-posterial orientation had the highest correlation to BV/TV (R(2) = 0.80, p < 0.001) and trabecular thickness (R(2) = 0.71, p < 0.001) at the frequency band centered at 1.3 MHz. The attenuation in the first frequency band was the most sensitive to the trabecular number (R(2) = 0.71, p < 0.001) and trabecular separation (R(2) = 0.80, p < 0.001). No significant correlation was observed for the attenuation in medial-lateral orientation across the four frequency bands.

Quantitative ultrasound noninvasive investigation of trabecular organization and orientation

Osteoporosis is a silent disease responsible for over a million fragility fractures per year. Current diagnostics rely heavily on bone density measurements. While clinical diagnostics rely on x-ray BMD, density measures alone are not sufficient for fracture risk prediction. Quantitative Ultrasound has emerged as an alternative measure, providing more inherent material information than simple density. To date research attempts to reduce variability in ultrasound measures by limiting motion and orientation of samples. However, as we see here, it may be possible to use this dependence on internal trabecular orientation as an additional measure to track the changing mechanical environment inside the bone as Osteoporosis progresses.

Phase cancellation and aperture size on broadband ultrasonic attenuation for trabecular bone assessment using a 2-D confocal synthetic array

A scanning ultrasound measurement system was developed for bone assessment using a receiver with an ultra-small aperture size to limit the phase cancellation effects on the physical receiver itself. Results show that phase cancellation does have a significant effect on BUA (e.g., PS nBUA is 8.1% higher than PI nBUA). Receiver aperture size also influences the BUA reading for both PI and PS detection and smaller receiver aperture tends to result in higher BUA readings.

Local and Distant Intramedullary Pressure and Bone Strain by Dynamic Hydraulic Stimulation

Osteoporosis gives rise to fragile bones that have higher fracture risks due to diminished bone mass and altered bone microarchitecture [1]. Mechanical loading mediated bone adaptation has demonstrated promising potentials as a non-pharmacological alteration for both osteogenic response and attenuation of osteopenia [2]. Intramedullary pressure (ImP) has been proposed as a key factor for fluid flow initiation and mechanotransductive signal inductions in bone. It is also suggested that integration of strain signals over time allows low-level mechanical strain in the skeleton to trigger osteogenic activities. The potential bone fluid flow induced by strain and ImP mediates adaptive responses in the skeleton [3]. Previous in vivo studies using oscillatory electrical stimulations showed that dynamic muscle contractions can generate ImP and bone strain to mitigate disuse osteopenia in a frequency-dependent manner. To apply ImP alteration as a means for bone fluid flow regulation, it may be necessary to develop a new method that could couple external loading with internal bone fluid flow. In order to further study the direct effect of ImP on bone adaptation, it was hypothesized that external dynamic hydraulic stimulation (DHS) can generate ImP with minimal strain in a frequency-dependent manner. The aim of this study was to evaluate the immediate effects on local and distant ImP and bone strain induced by a novel, non-invasive dynamic external pressure stimulus in response to a range of loading frequencies.Copyright

Induced Intramedullary Pressure by Dynamic Hydraulic Stimulation and Its Potential in Attenuation of Bone Loss

Bone loss is a critical health problem of astronauts in long-term space missions. A growing number of evidence has pointed out bone fluid flow as a critical regulator in mechanotransductive signaling and bone adaptation. Intramedullary pressure (ImP) is a key mediator for bone fluid flow initiation and it influences the osteogenic signals within the skeleton. The potential ImP-induced bone fluid flow then triggers bone adaptation [1]. Previous in vivo study has demonstrated that ImP induced by oscillatory electrical stimulations can effectively mitigate disuse osteopenia in a frequency-dependent manner in a disuse rat model [2, 3]. In order to develop the translational potentials of ImP, a non-invasive intervention with direct fluid flow coupling is necessary to develop new treatments for microgravity-induced osteopenia/osteoporosis.© 2011 ASME

Mitigation of bone loss and muscle atrophy by dynamic hydraulic pressure stimulation

Osteoporosis is a skeletal disease that leads to decreased bone mass and changes in bone microstructure, which results in weaker bones that are more susceptible for fractures [1]. Disuse osteoporosis often occurs in elderly, long-term bed-rest patients, and long-duration spaceflight. Muscle atrophy is often associated with this disease [5]. In order to enhance bone quality and muscle strength, effective clinical treatments, particularly using non-pharmacological approach, are urgently called for. Mechanical strain and intramedullary pressure (ImP) provide mechanotransductive signals that are able to trigger bone adaptation. It has been suggested that strain signals may integrate and allow low-level strain to trigger osteogenic activities in the skeleton [2]. ImP distribution may also influence the mechanotransductory signaling levels in bone. Bone fluid flow is potentially induced by strain and ImP, leading to skeletal adaptive responses [3]. Prior studies showed that functional disuse bone loss can be prevented through noninvasive oscillatory electrical stimulation in a rat hindlimb suspension model [4, 5]. Such stimuli create muscle contraction that may build up pressure gradient in the vascular bed and further increase ImP in bone. As a potential of translational studies for osteoporosis and osteopenia, a non-invasive manner is necessary for the development of new treatments. The objectives of this study were to 1) develop a novel, non-invasive external dynamic hydraulic pressure muscle stimulation for bone quality enhancement; and 2) to evaluate the effects of this dynamic hydraulic pressure stimulation on muscle strength to further delineate the bone fluid flow mechanism.