STUDY DESIGN: Controlled laboratory study. OBJECTIVES: To measure the architectural properties of rat supraspinatus muscle after a complete detachment of its distal tendon. METHODS: Supraspinatus muscles were released from the left humerus of 29 Sprague-Dawley rats (mass, 400-450 g), and the animals were returned to cage activity for 2 weeks (n = 12), 4 weeks (n = 9), or 9 weeks (n = 8), before euthanasia. Measurements of muscle mass, pennation angle, fiber bundle length (sarcomere number), and sarcomere length permitted calculation of normalized fiber length, serial sarcomere number, and physiological cross-sectional area. RESULTS: Coronal oblique sections of the supraspinatus confirmed surgical transection of the supraspinatus muscle at 2 weeks, with reattachment by 4 weeks. Muscle mass and length were significantly lower in released muscles at 2 weeks, 4 weeks, and 9 weeks. Sarcomere lengths in released muscles were significantly shorter at 2 weeks but not different by 4 weeks. Sarcomere number was significantly reduced at 2 and 4 weeks, but returned to control values by 9 weeks. The opposing effects of smaller mass and shorter fibers produced significantly smaller physiological cross-sectional area at 2 weeks, but physiological cross-sectional area returned to control levels by 4 weeks. CONCLUSIONS: Release of the supraspinatus muscle produced early radial and longitudinal atrophy of the muscle. The functional implications of these adaptations would be most profound at early time points (particularly relevant for rehabilitation), when the muscle remains smaller in cross-sectional area and, due to reduced sarcomere number, would be forced to operate over a wider range of the length-tension curve and at higher velocities, all adaptations resulting in compromised force-generating capacity. These data are relevant to physical therapy because they provide tissue-level insights into impaired muscle and shoulder function following rotator cuff injury.

J Orthop Sports Phys Ther 2010;40(11):729-735, Epub 6 August 2010. doi:10.2519/jospt.2010.3279

KEY WORDS: muscle plasticity, rotator cuff, shoulder, tendinopathy

SYNOPSIS: The organization of fibers within a muscle (architecture) defines the performance capacity of that muscle. In the current commentary, basic architectural terms are reviewed in the context of the major hip muscles and then specific illustrative examples relevant to lower extremity rehabilitation are presented. These data demonstrate the architectural and functional specialization of the hip muscles, and highlight the importance of muscle physiology and joint mechanics when evaluating and treating musculoskeletal disorders.

J Orthop Sports Phys Ther 2010;40(2):95-102. doi:10.2519/jospt.2010.3302

KEY WORDS: exercise, gluteus maximus, gluteus medius, hip, rehabilitation

Study Design: Single-group, repeated-measures design. Objective: To compare patellofemoral joint kinematics during weight-bearing and non–weight-bearing knee extension in persons with lateral subluxation of the patella. Background: The only previous study to quantify differences in patellofemoral joint kinematics during weight-bearing and non–weight-bearing tasks was limited in that static loading conditions were utilized. Differences in patellofemoral joint kinematics between weight-bearing and non–weight-bearing conditions have not been quantified during dynamic movement. Methods and Measures: Six females with a diagnosis of patellofemoral pain and lateral subluxation of the patella participated. Using kinematic magnetic resonance imaging, axial images of the patellofemoral joint were obtained as subjects extended their knees from 45° to 0° during non–weight-bearing (5% body weight resistance) and weight-bearing (unilateral squat) conditions. Measurements of patellofemoral joint relationships (medial/lateral patellar displacement and patellar tilt), as well as femur and patella rotations relative to an external reference system (ie, the image field of view), were obtained at 3° increments during knee extension. Results: During non–weight-bearing knee extension, lateral patellar displacement was more pronounced than during the weight-bearing condition between 30° and 12° of knee extension, with statistical significance being reached at 27°, 24°, and 21°. No differences in lateral patellar tilt were observed between conditions (P = .065). During the weight-bearing condition, internal femoral rotation was significantly greater than during the non–weight-bearing condition as the knee extended from 18° to 0°. During the non–weight-bearing condition, the amount of lateral patellar rotation was significantly greater than during the weight-bearing condition throughout the range of motion tested. Conclusions: The results of this study demonstrated that lateral patellar displacement was more pronounced during non–weight-bearing knee extension compared to weight-bearing knee extension in persons with lateral patellar subluxation. In addition, the results of this investigation suggest that the patellofemoral joint kinematics during non–weight-bearing could be characterized as the patella rotating on the femur, while the patellofemoral joint kinematics during the weight-bearing condition could be characterized as the femur rotating underneath the patella.

J Orthop Sports Phys Ther. 2003;33(11):677-685.
 

Key Words: magnetic resonance imaging, patellar tracking, patellofemoral joint

At the time this study was conducted, there were no financial conflicts of interest with any of the authors. Subsequently, a version of the device described in this manuscript was manufactured and marketed by Matsumoto Prosthetics and Orthotics Manufacturing Co, LTD, located in Nagoya, Japan. Mr. Ota has a financial interest with this arrangement and acknowledges a potential conflict of interest.

Study Design: Repeated-measures, within-subject design.
Objective: To assess the concurrent criterion-related validity and reliability of a clinical device to quantify lateral patellar displacement.
Background: Excessive lateral displacement of the patella is an impairment that is widely associated with patellofemoral pain and/or pathology. Currently, no valid or reliable clinical method to assess lateral patellar displacement has been described in the literature.
Methods and Measures: A total of 26 individuals (14 asymptomatic and 12 symptomatic; mean ± SD age, 27 ± 4 years) participated in the validity portion of this study, while an additional 10 asymptomatic volunteers (mean ± SD age, 28 ± 5 years) participated in the reliability portion. Lateral displacement of the patella was assessed using a custom-designed patellofemoral arthrometer (PFA) and was compared to actual position of the patella as determined by magnetic resonance imaging (MRI). Both PFA and MRI measurements of lateral patellar displacement were made with the knee extended and the quadriceps contracted. The intraclass correlation coefficient (ICC) was used to assess the level of agreement between the PFA and MRI measurements, as well as the intrarater and interrater reliability of the PFA measurements.
Results: The ICC assessing the level of agreement between the MRI and PFA measures of lateral patellar displacement was good (0.86). Excellent intratester (ICC, 0.96 and 0.97) and intertester reliability (ICC, 0.92) were demonstrated.
Conclusion: Our results suggest that reasonable estimations of lateral patellar displacement can be obtained using the PFA.

J Orthop Sports Phys Ther. 2006;36(9):645-652. doi:10.2519/jospt.2006.2263

Key Words: knee, magnetic resonance imaging, patellar tracking, patellofemoral  joint