Nicholas A. T. Brown

A Prospective Randomized Clinical Trial Comparing Arthroscopic Single- and Double-Row Rotator Cuff Repair Magnetic Resonance Imaging and Early Clinical Evaluation

Background Double-row arthroscopic rotator cuff repair has become more popular, and some studies have shown better footprint coverage and improved biomechanics of the repair. Hypothesis Double-row rotator cuff repair leads to superior cuff integrity and early clinical results compared with single-row repair. Study Design Randomized controlled trial; Level of evidence, 1. Methods Forty patients were randomized to either single-row or double-row rotator cuff repair at the time of surgical intervention. Patients were followed with clinical measures (UCLA, Constant, WORC, SANE, ASES, as well as range of motion, internal rotation strength, and external rotation strength). Magnetic resonance imaging (MRI) studies were performed on each shoulder preoperatively, 6 weeks, 3 months, and 1 year after repair. Results Mean anteroposterior tear size by MRI was 1.8 cm. A mean of 2.25 anchors for single row (SR) and 3.2 for double row (DR) were used. There were 2 retears at 1 year in each group. There were 2 additional cases that had severe thinning in the DR repair group at 1 year. The MRI measurements of footprint coverage, tendon thickness, and tendon signal showed no significant differences between the 2 repair groups. At 1 year, there were no differences in any of the postoperative measures of motion or strength. At 1 year, mean WORC (SR, 84.8; DR, 87.9), Constant (SR, 77.8; DR, 74.4), ASES (SR, 85.9; DR, 85.5), UCLA (SR, 28.6; DR, 29.5), and SANE (SR, 90.9; DR, 89.9) scores showed no significant differences between groups. Conclusions No clinical or MRI differences were seen between patients repaired with a SR or DR technique.

Effect of Running Speed on Lower Limb Joint Kinetics

PURPOSE Knowledge regarding the biomechanical function of the lower limb muscle groups across a range of running speeds is important in improving the existing understanding of human high performance as well as in aiding in the identification of factors that might be related to injury. The purpose of this study was to evaluate the effect of running speed on lower limb joint kinetics. METHODS Kinematic and ground reaction force data were collected from eight participants (five males and three females) during steady-state running on an indoor synthetic track at four discrete speeds: 3.50±0.04, 5.02±0.10, 6.97±0.09, and 8.95±0.70 m·s. A standard inverse-dynamics approach was used to compute three-dimensional torques at the hip, knee, and ankle joints, from which net powers and work were also calculated. A total of 33 torque, power, and work variables were extracted from the data set, and their magnitudes were statistically analyzed for significant speed effects. RESULTS The torques developed about the lower limb joints during running displayed identifiable profiles in all three anatomical planes. The sagittal-plane torques, net powers, and work done at the hip and knee during terminal swing demonstrated the largest increases in absolute magnitude with faster running. In contrast, the work done at the knee joint during stance was unaffected by increasing running speed, whereas the work done at the ankle joint during stance increased when running speed changed from 3.50 to 5.02 m·s, but it appeared to plateau thereafter. CONCLUSIONS Of all the major lower limb muscle groups, the hip extensor and knee flexor muscles during terminal swing demonstrated the most dramatic increase in biomechanical load when running speed progressed toward maximal sprinting.

Patellofemoral Contact Pressures and Lateral Patellar Translation After Medial Patellofemoral Ligament Reconstruction

Background Overtensioning of medial patellofemoral ligament reconstructions may lead to adverse surgical outcomes. Hypothesis Increasing tension on a medial patellofemoral ligament graft will increase patellofemoral contact forces and decrease lateral patellar translation. Study Design Controlled laboratory study. Methods Patellofemoral contact pressures were measured in 8 fresh-frozen cadaveric knees before and after transection of the medial patellofemoral ligament and after a standardized reconstruction surgery. Contact pressures were measured at 3 knee angles (30°, 60°, and 90°) and under 3 levels of tension applied to the graft (2, 10, and 40 N). For each condition, patellar translation was measured at 30° of knee flexion as a 22-N lateral force was applied. Results Graft tension of 2 N restored normal translation, but 10 N and 40 N significantly restricted motion (5.2 mm and 1.9 mm, respectively). Compared with the intact knee, medial patellofemoral contact pressures significantly increased (P < .05) when 40 N of tension was applied to the reconstruction. Medial contact pressures were restored to normal with 2 N of graft tension. Lateral patellar translation was significantly greater (P < .05) after the medial patellofemoral ligament was cut (16.3 mm) compared with intact (7.7 mm). Conclusion Low (2-N) tension applied to a medial patellofemoral ligament reconstruction stabilized the patella and did not increase medial patellofemoral contact pressures. Higher loads (10 N and 40 N) progressively restricted lateral patellar translation and inappropriately redistributed patellofemoral contact pressures. Clinical Relevance Overtensioning can be avoided by applying low loads to medial patellofemoral ligament reconstructions, which reestablished normal translation and patellofemoral contact pressures.

Mechanics of the human hamstring muscles during sprinting.

PURPOSE An understanding of hamstring mechanics during sprinting is important for elucidating why these muscles are so vulnerable to acute strain-type injury. The purpose of this study was twofold: first, to quantify the biomechanical load (specifically, musculotendon strain, velocity, force, power, and work) experienced by the hamstrings across a full stride cycle; and second, to determine how these parameters differ for each hamstring muscle (i.e., semimembranosus (SM), semitendinosus (ST), biceps femoris long head (BF), biceps femoris short head (BF)). METHODS Full-body kinematics and ground reaction force data were recorded simultaneously from seven subjects while sprinting on an indoor running track. Experimental data were integrated with a three-dimensional musculoskeletal computer model comprised of 12 body segments and 92 musculotendon structures. The model was used in conjunction with an optimization algorithm to calculate musculotendon strain, velocity, force, power, and work for the hamstrings. RESULTS SM, ST, and BF all reached peak strain, produced peak force, and formed much negative work (energy absorption) during terminal swing. The biomechanical load differed for each hamstring muscle: BF exhibited the largest peak strain, ST displayed the greatest lengthening velocity, and SM produced the highest peak force, absorbed and generated the most power, and performed the largest amount of positive and negative work. CONCLUSIONS As peak musculotendon force and strain for BF, ST, and SM occurred around the same time during terminal swing, it is suggested that this period in the stride cycle may be when the biarticular hamstrings are at greatest injury risk. On this basis, hamstring injury prevention or rehabilitation programs should preferentially target strengthening exercises that involve eccentric contractions performed with high loads at longer musculotendon lengths.

Joint-specific power production and fatigue during maximal cycling

Cycling power decreases substantially during a maximal cycling trial of just 30s. It is not known whether movement patterns and joint powers produced at each joint decrease to a similar extent or if each joint exhibits an individual fatigue profile. Changes in movement patterns and/or joint powers associated with overall task fatigue could arise from several different mechanisms or from a complex interplay of these mechanisms. The purpose of this investigation was to determine the changes in movement and power at each joint during a fatiguing cycling trial. Thirteen trained cyclists performed a 30s maximal cycling trial on an isokinetic cycle ergometer at 120rpm. Pedal forces and limb kinematics were recorded. Joint powers were calculated using a sagittal plane inverse dynamics model and averaged for the initial, middle, and final three second intervals of the trial, and normalized to initial values. Relative ankle plantar flexion power was significantly less than all other joint actions at the middle interval (51+/-5% of initial power; p=0.013). Relative ankle plantar flexion power for the final interval (37+/-3%) was significantly less than the relative knee flexion and hip extension power (p=0.010). Relative knee extension power (41+/-5%) was significantly less than relative hip extension power (55+/-4%) during the final three second interval (p=0.045). Knee flexion power (47+/-5%) did not differ from relative hip extension power (p=0.06). These changes in power were accompanied by a decrease in time spent extending by each joint with fatigue (i.e., decreased duty cycle, p<0.03). While central mechanisms may have played a role across all joints, because the ankle fatigued more than the hip and knee joints, either peripheral muscle fatigue or changes in motor control strategies were identified as the potential mechanisms for joint-specific fatigue during a maximal 30s cycling trial.

Force- and moment-generating capacities of muscles in the distal forelimb of the horse.

A detailed musculoskeletal model of the distal equine forelimb was developed to study the influence of musculoskeletal geometry (i.e. muscle paths) and muscle physiology (i.e. force–length properties) on the force‐ and moment‐generating capacities of muscles crossing the carpal and metacarpophalangeal joints. The distal forelimb skeleton was represented as a five degree‐of‐freedom kinematic linkage comprised of eight bones (humerus, radius and ulna combined, proximal carpus, distal carpus, metacarpus, proximal phalanx, intermediate phalanx and distal phalanx) and seven joints (elbow, radiocarpal, intercarpal, carpometacarpal, metacarpophalangeal (MCP), proximal interphalangeal (pastern) and distal interphalangeal (coffin)). Bone surfaces were reconstructed from computed tomography scans obtained from the left forelimb of a Thoroughbred horse. The model was actuated by nine muscle–tendon units. Each unit was represented as a three‐element Hill‐type muscle in series with an elastic tendon. Architectural parameters specifying the force‐producing properties of each muscle–tendon unit were found by dissecting seven forelimbs from five Thoroughbred horses. Maximum isometric moments were calculated for a wide range of joint angles by fully activating the extensor and flexor muscles crossing the carpus and MCP joint. Peak isometric moments generated by the flexor muscles were an order of magnitude greater than those generated by the extensor muscles at both the carpus and the MCP joint. For each flexor muscle in the model, the shape of the maximum isometric joint moment–angle curve was dominated by the variation in muscle force. By contrast, the moment–angle curves for the muscles that extend the MCP joint were determined mainly by the variation in muscle moment arms. The suspensory and check ligaments contributed more than half of the total support moment developed about the MCP joint in the model. When combined with appropriate in vivo measurements of joint kinematics and ground‐reaction forces, the model may be used to determine muscle–tendon and joint–reaction forces generated during gait.

A governing relationship for repetitive muscular contraction

During repetitive contractions, muscular work has been shown to exhibit complex relationships with muscle strain length, cycle frequency, and muscle shortening velocity. Those complex relationships make it difficult to predict muscular performance for any specific set of movement parameters. We hypothesized that the relationship of impulse with cyclic velocity (the product of shortening velocity and cycle frequency) would be independent of strain length and that impulse-cyclic velocity relationships for maximal cycling would be similar to those of in situ muscle performing repetitive contraction. Impulse and power were measured during maximal cycle ergometry with five cycle-crank lengths (120-220mm). Kinematic data were recorded to determine the relationship of pedal speed with joint angular velocity. Previously reported in situ data for rat plantaris were used to calculate values for impulse and cyclic velocity. Kinematic data indicated that pedal speed was highly correlated with joint angular velocity at the hip, knee, and ankle and was, therefore, considered a valid indicator of muscle shortening velocity. Cycling impulse-cyclic velocity relationships for each crank length were closely approximated by a rectangular hyperbola. Data for all crank lengths were also closely approximated by a single hyperbola, however, impulse produced on the 120mm cranks differed significantly from that on all other cranks. In situ impulse-cyclic velocity relationships exhibited similar characteristics to those of cycling. The convergence of the impulse-cyclic velocity relationships from most crank and strain lengths suggests that impulse-cyclic velocity represents a governing relationship for repetitive muscular contraction and thus a single equation can predict muscle performance for a wide range of functional activities. The similarity of characteristics exhibited by cycling and in situ muscle suggests that cycling can serve as a window though which to observe basic muscle function and that investigators can examine similar questions with in vivo and in situ models.

Static versus dynamic loading in the mechanical modulation of vertebral growth.

Study Design. Measures of absolute and relative growth modulation were used to determine the effects of static and dynamic asymmetric loading of vertebrae in the rat tail. Objectives. To quantify the differences between static and dynamic asymmetric loading in vertebral bone growth modulation. Summary of Background Data. The creation and correction of vertebral wedge deformities have been previously described in a rat-tail model using static loading. The effects of dynamic loading on growth modulation in the spine have not been characterized. Methods. A total of 36 immature Sprague-Dawley rats were divided among four different groups: static loading (n = 12, 0.0 Hz), dynamic loading (n = 12, 1.0 Hz), sham operated (n = 6), and growth controls (n = 6). An external fixator was placed across the sixth and eighth caudal vertebrae as the unviolated seventh caudal vertebra was evaluated for growth modulation. Static or dynamic asymmetric loads were applied at a loading magnitude of 55% body weight. After 3 weeks of loading, growth modulation was assessed using radiographic measurements of vertebral wedge angles and vertebral body heights. Results. The dynamically loaded rats had a final average wedge deformity of 15.2° ± 6.4°, which was significantly greater than the statically loaded rats whose final deformity averaged 10.3° ± 3.7° (P < 0.03). The deformity in both groups was statistically greater than the sham-operated (1.1° ± 2.0°) and growth control rats (0.0° ± 1.0°) (P < 0.001). The longitudinal growth was significantly lower on the concavity compared with the convexity in both the dynamically (0.34 ± 0.23 mm vs. 0.86 ± 0.23 mm) and statically (0.46 ± 0.19 mm vs. 0.83 ± 0.32 mm) loaded rats (P < 0.001). These growth rates were significantly less than the sham operated and growth control rats (P < 0.001). Conclusions. A variety of fusionless scoliosis implant strategies have been proposed that use both rigid and flexible implants to modulate vertebral bone growth. The results from this study demonstrate that dynamic loading of the vertebrae provides the greatest growth modulation potential.

In vivo behavior of the human soleus muscle with increasing walking and running speeds

The interaction between the muscle fascicle and tendon components of the human soleus (SO) muscle influences the capacity of the muscle to generate force and mechanical work during walking and running. In the present study, ultrasound-based measurements of in vivo SO muscle fascicle behavior were combined with an inverse dynamics analysis to investigate the interaction between the muscle fascicle and tendon components over a broad range of steady-state walking and running speeds: slow-paced walking (0.7 m/s) through to moderate-paced running (5.0 m/s). Irrespective of a change in locomotion mode (i.e., walking vs. running) or an increase in steady-state speed, SO muscle fascicles were found to exhibit minimal shortening compared with the muscle-tendon unit (MTU) throughout stance. During walking and running, the muscle fascicles contributed only 35 and 20% of the overall MTU length change and shortening velocity, respectively. Greater levels of muscle activity resulted in increasingly shorter SO muscle fascicles as locomotion speed increased, both of which facilitated greater tendon stretch and recoil. Thus the elastic tendon contributed the majority of the MTU length change during walking and running. When transitioning from walking to running near the preferred transition speed (2.0 m/s), greater, more economical ankle torque development is likely explained by the SO muscle fascicles shortening more slowly and operating on a more favorable portion (i.e., closer to the plateau) of the force-length curve.

Acetabular cartilage thickness: accuracy of three-dimensional reconstructions from multidetector CT arthrograms in a cadaver study.

PURPOSE To prospectively quantify the accuracy of hip cartilage thickness estimated from three-dimensional (3D) surfaces, generated by segmenting multidetector computed tomographic (CT) arthrograms by using direct physical measurements of cartilage thickness as the reference standard. MATERIALS AND METHODS Four fresh-frozen cadaver hip joints from two male donors, ages 43 and 46 years, were obtained; institutional review board approval for cadaver research was also obtained. Sixteen holes were drilled perpendicular to the cartilage of four cadaveric acetabula (two specimens). Hip capsules were surgically closed, injected with contrast material, and scanned by using multidetector CT. After scanning, 5.3-mmcores were harvested concentrically at each drill hole and cartilage thickness was measured with a microscope. Cartilage was reconstructed in 3D by using commercial software. Segmentations were repeated by two authors. Reconstructed cartilage thickness was determined by using a published algorithm. Bland-Altman plots and linear regression were used to assess accuracy. Repeatability was quantified by using the coefficient of variation, intraclass correlation coefficient (ICC), repeatability coefficient, and percentage variability. RESULTS Cartilage was reconstructed to a bias of -0.13 mm and a repeatability coefficient of + or - 0.46 mm. Regression of the scatterplots indicated a tendency for multidetector CT to overestimate thickness. Intra- and interobserver repeatability were very good. For intraobserver correlation, the coefficient of variation was 14.80%, the ICC was 0.88, the repeatability coefficient was 0.55 mm, and the percentage variability was 11.77%. For interobserver correlation, the coefficient of variation was 13.47%, the ICC was 0.90, the repeatability coefficient was 0.52 mm, and the percentage variability was 11.63%. CONCLUSION Assuming that an accuracy of approximately + or - 0.5 mm is sufficient, reconstructions of cartilage geometry from multidetector CT arthrographic data could be used as a preoperative surgical planning tool.