Myotendinous Unit Research Articles

The Gluteus Medius Experiences Significant Excursion With Hip Flexion

To evaluate the effect of hip flexion and rotation on excursion of the gluteus medius (Gmed) and minimus (Gmin) myotendinous unit. Seven hips from 4 cadaveric specimens (males, 68.5 ± 18.3 years old) were dissected to isolate the Gmed posterior and lateral insertions and the Gmin proximal and distal insertions. Sutures were placed from tendon insertions through origins created in the iliac fossa to simulate the myotendinous unit. A load of 10N was applied. Myotendinous excursion was measured at 10° hip extension and 0°, 45°, and 90° of hip flexion in neutral rotation, and from maximum internal and external rotation in 90° flexion. The amount of abduction and rotation was also measured at each flexion position with 20N applied to each tendon. Repeated-measures analysis of variance with Tukey post hoc was used for statistics. Gmed-lateral excursion ranged from 2.4 ± 0.4 mm in 10° of hip extension to 23.0 ± 1.5 mm in 90° of flexion (P < .001), and Gmed-posterior excursion ranged from 0.92 ± 0.5 mm in 10° of extension to 38.1 ± 1.1 mm in 90° of flexion (P < .001). Gmin excursion shortened with hip flexion from 4.2 ± 0.3 mm in 10° of extension to-0.2 ± 1.5 mm in 90° of flexion (Gmin-prox: P= .525, Gmin-distal: P < .001). At 90° flexion from maximum internal to maximum external rotation, Gmin-distal and proximal demonstrated a 92.6% and 51.3% increase in excursion, respectively (P < .001). Gmed-lateral and Gmed-posterior demonstrated 49.4% and 23.1% increase in excursion with external rotation, respectively (P < .001). The Gmed myotendinous unit undergoes significant excursion with hip flexion, whereas both Gmed and Gmin had significant excursion with femoral external rotation in 90° flexion. It is important to understand whether active or passive hip flexion or rotation in the early postoperative period causes excessive strain to an abductor tendon repair. We found that consideration should be given to limit flexion after Gmed repair and external rotation after Gmed or Gmin repairs.

Three-Dimensional Software- and MR-Imaging-Based Muscle Volumetry Reveals Overestimation of Supraspinatus Muscle Atrophy Using Occupation Ratios in Full-Thickness Tendon Tears.

Supraspinatus muscle atrophy is widely determined from oblique-sagittal MRI by calculating the occupation ratio. This ex vivo and clinical study aimed to validate the accuracy of 3D software- and MR-imaging-based muscle volumetry, as well as to assess the influence of the tear pattern on the occupation ratio. Ten porcine muscle specimens were volumetrized using the physical water displacement volumetry as a standard of reference. A total of 149 individuals with intact supraspinatus tendons, partial tears, and full-thickness tears had 3T MRI. Two radiologists independently determined occupation ratio values. An excellent correlation with a Pearson’s r of 0.95 for the variables physical volumetry using the water displacement method and MR-imaging-based muscle volumetry using the software was found and formed the standard of reference for the patient study. The inter-reader reliability was 0.92 for occupation ratios. The correlation between occupation ratios and software-based muscle volumes was good in patients with intact tendons (0.84) and partial tears (0.93) but considerably lower in patients with full-thickness tears (0.68). Three-dimensional-software- and MR-imaging-based muscle volumetry is reliable and accurate. Compared to 3D muscle volumetry, the occupation ratio method overestimates supraspinatus muscle atrophy in full-thickness tears, which is most likely due to the medial retraction of the myotendinous unit.

Epimuscular Myofascial Force Transmission between Nerve and Myotendinous Unit: A Shear-Wave Elastography Study

Epimuscular Myofascial Force Transmission between Nerve and Myotendinous Unit: A Shear-Wave Elastography Study

A comprehensive review of the normal, abnormal, and post-operative MRI appearance of the distal biceps brachii.

The biceps brachii myotendinous unit is a common source of shoulder, arm, and elbow pain. Its complex anatomy can present a challenge when interpreting MR images. We discuss the clinical and imaging presentations of injury related to the proximal biceps brachii separately in another manuscript. The purpose of this manuscript is to review the distal biceps anatomy along with pathology and post-operative appearance as seen on MRI.

A comprehensive review of the normal, abnormal, and post-operative MRI appearance of the proximal biceps brachii.

The biceps brachii myotendinous unit, particularly the long head of the biceps tendon and its labral attachment, is a common cause of shoulder and arm pain. Its complex anatomy and normal variations can present a challenge when interpreting MR images. The purpose of this manuscript is to review the proximal biceps anatomy, variants, pathology, and post-operative appearance as seen on MRI. Recent data regarding the accuracy of clinical examination and MRI will be summarized.

Macroscopic and ultrasonographic anatomy of the rotator cuff layers.

Aim:The aim of the study was to determine the thickness of the tendinous and capsuloligamentous layers in the supraspinatus and infraspinatus zones of the shoulder.Materials and methods:Anatomical and ultrasonographic assessment of three fresh anatomical specimens consisting of the humeral head together with the capsuloligamentous layer called the superior complex and the supraspinatus and infraspinatus myotendinous units cut off at the level of the scapular glenoid rim. The first specimen was dissected on the length of approx. 10 mm from the glenoid insertion – the superior complex insertional zone to the scapula. Distally anterior (coraco-humeral and gleno-humeral superior ligaments) and posterior (gleno-humeral superior posterior ligament) limbs are connected by a transversely oriented ligament called the rotator cuff cable. This structure, together with the rest of the superior complex, belongs to the capsuloligamentous layer of the rotator cuff. The two other specimens were dissected (superior complex from the myotendinous units) from the level of the glenoid rim to the humeral insertion. Then the three specimens were scanned by ultrasound in a water bath and the measurements of both distinct layers were taken.Results:The rotator cuff in the supraspinatus and infraspinatus zone is a two-layer structure. The thickness of the tendinous and the capsuloligamentous layer is comparable.Conclusions:It may be concluded that the rotator cuff in the supraspinatus and infraspinatus zone is a two-layer structure, with the outer myotendinous layer, and the inner capsuloligamentous layer, which is called the superior complex. Since the thickness of these layers is comparable, it is important to bear in mind that the superior complex is an important part of shoulder biomechanics. Two different structures are found here – tendinous (dynamic) and capsuloligamentous (passive).

Pseudo-Volkmann Contracture: A Case Report and Review of the Current Literature.

Background:Unlike the usual Volkmann contracture as a complication of pediatric forearm fracture, pseudo-Volkmann contracture is not a sequela of ischemia, but rather of a mechanical entrapment of the flexor myotendinous units in the fracture or adhesions.Methods:PubMed search of the English literature was performed using the terminology entrapment and fracture and pseudo-Volkmann.Results:Thirteen articles were identified that described cases of pseudo-Volkmann contracture in pediatric both-bone forearm fractures. Totally, 26 cases were reported in the English literature. Additionally, we describe two more cases in detail.Discussion:Pseudo-Volkmann contracture is well described but uncommon. It most commonly involves the ring finger flexor digitorum superficialis but can occur in all fingers. This entrapment can be identified acutely with intentional examination by confirming full passive motion of the fingers after preferred treatment of both-bone forearm fractures in the pediatric patient. When contracture is identified on examination, surgical intervention to clear the entrapment from the fracture is effective and produces excellent results.

Rotator cuff repair: challenges and solutions

Each year, 250,000 rotator cuff repairs are performed in the United States at a cost of $3 billion. Despite advancements in repair techniques and rehabilitation, 20%-70% of repairs continue to undergo structural failure; however, there is a poor correlation between clinical and structural outcomes, both before and after surgery. Failure in continuity, or retraction of the repair site without a structural defect, is likely a common phenomenon after rotator cuff repair, and this retraction of the myotendinous unit and interposing scar tissue may be one explanation for the discordance between clinical and structural outcomes. Scaffolds, both synthetic and biologic, have shown promise in both augmentation of repairs and interposition of irreparable tears, but most studies are small retrospective case series without control groups. Future efforts will need to determine the ideal indications for use, methods of application, and comparative effectiveness between the devices. Platelet-rich plasma also has potential to improve rotator cuff healing, but current limitations include the significant variation in preparation methods, biologic makeup, and application methods. Future work may help us understand whether application of platelet-rich plasma and its growth factors should be done at the time of surgery or later during a more advanced stage of healing. Regardless of the device or technique, mechanical and/or biologic augmentation of rotator cuff repairs requires the surgeon to be technically proficient in its use and aware of its associated increased operative time and cost. In order to justify the use of these technologies and their associated incremental cost, we must demonstrate efficacy in improving both clinical and structural outcomes.

Animal model for chronic massive rotator cuff tear: behavioural and histologic analysis.

Massive rotator cuff tears (MRCT) are usually chronic lesions that present associated degenerative changes of the myotendinous unit that have been implicated in limitations for surgical repair. In order to develop effective therapies, it is important to establish animal models that mimic the hallmarks of the injury itself. Therefore, in the present work, we aimed to (1) optimize a rodent animal model of MRCT that closely reproduces the fatty infiltration of the cuff muscles seen in humans and (2) describe the effects of unilateral or bilateral lesion in terms of histology and behaviour. Massive tear was defined as two rotator cuff tendons-supraspinatus and infraspinatus-section. Twenty-one Wistar rats were randomly assigned to four groups: bilateral lesion (five animals), right-sided unilateral lesion (five animals), left-sided unilateral lesion (five animals) and control (six animals). Behaviour was analyzed with open field and staircase test, 16 weeks after lesion. After that, animals were killed, and the supraspinatus and infraspinatus muscles were processed. Histologic analysis revealed adipocytes, fatty infiltration and atrophy in the injured side with a greater consistency of these degenerative changes in the bilateral lesion group. Behaviour analysis revealed a significant functional impairment of the fine motor control of the forepaw analyzed in staircase test where the number of eaten pellets was significantly higher in sham animals (sham = 7 ± 5.0; left unilateral = 2.6 ± 3.0; right unilateral = 0 ± 0; and bilateral = 0 ± 0, p < 0.05). A trend to reach a lower level of steps, in more injured animals, was also observed (sham animals = 3 ± 1.6 > left unilateral = 2 ± 2.1 > right unilateral = 0.8 ± 1.3 > bilateral = 0.8 ± 1.1). The present study has been able to establish an animal model that disclosed the hallmarks of MRCT. This can now be used as a valuable, cost-effective, pre-clinical instrument to assist in the development of advanced tissue engineered strategies. Moreover, this animal model overcomes some of the limitations of those that have been reported so far and thus represents a more reliable source for the assessment of future therapeutic strategies with potential clinical relevance.

The Muscle Stretch Reflex throughout the Menstrual Cycle

The significant sex disparity in sports-related knee injuries may be due to underlying differences in motor control. Although the development of sex-specific movement patterns is likely multifactorial, this study specifically focuses on the potential modulatory role of sex hormones. This study aimed to investigate the muscle stretch reflex (MSR) across the menstrual cycle. We hypothesized that the MSR would fluctuate throughout the menstrual cycle and that the lowest response would correspond with peak concentrations of estrogen. Nineteen healthy women age 18-35 yr participated in this study: 8 eumenorrheic women and 11 women taking oral contraceptives. Serum estradiol and progesterone concentrations, anterior knee laxity (AKL), and the MSR response of the quadriceps muscles were measured three times during the menstrual cycle. The MSR response of the rectus femoris (RF) varied significantly across the menstrual cycle in both groups. Specifically, the RF MSR response was 2.4 times lower during the periovulatory phase when compared with the luteal phase (P = 0.007). The same trend was seen in the vastus medialis, but this did not reach statistical significance (P = 0.070). The MSR response of the vastus lateralis did not change significantly across the menstrual cycle (P = 0.494). A mixed model comparison did not show an association between endogenous concentrations of estradiol and progesterone, exposure to hormonal contraceptives or AKL, and the MSR response for any muscle. Our results demonstrate that the RF MSR response varies throughout the menstrual cycle with the lowest response around the time of ovulation. Additional research is needed to clarify the exact relationship between sex hormones, AKL, and MSR response and to determine the specific origin of the change along the monosynaptic reflex arc.

Biomechanical testing of small versus large lesser tuberosity osteotomies: effect on gap formation and ultimate failure load

Subscapularis muscle dysfunction after total shoulder arthroplasty (TSA) can be a devastating complication. Recent biomechanical and clinical results suggest the superiority of lesser tuberosity osteotomy (LTO) over subscapularis tenotomy; however, disagreement over the best repair technique remains. This study aimed to characterize the strength of 2 novel repair techniques for LTO fixation compared with standard tenotomy and dual-row tuberosity osteotomies during TSA. Twenty fresh frozen cadaveric shoulders were dissected of all soft tissues except the humeri and attached subscapularis myotendinous unit. Humeri and subscapularis muscle belly were secured to a materials testing frame and subjected to cyclic loading, followed by load to failure for characterization of gap formation, ultimate failure load, and mechanism of failure. Repair techniques investigated were traditional subscapularis tenotomy and dual-row fleck LTO compared with novel techniques of single-cable and 2-suture large LTO repairs. No significant difference in ultimate failure load was noted among the repair techniques (P=.565). The tenotomy repair (6.0±3.9mm) displayed significantly greater gapping in response to increasing load than LTO repair techniques (P<.05). No significant difference was noted between any LTO repairs at specific loads during cyclic testing (P>.05). Our study displayed superior repair integrity of LTO vs tenotomy repairs. The advantages of the 2-suture large LTO technique over other LTO techniques include its simple technique, with a minimum amount of suture, avoidance of metallic hardware, and greater access to the glenoid, while providing comparable repair stability. Further research is warranted to fully evaluate these new techniques.

Imaging Lesions of the Lateral Hip

The lateral aspect of the hip is composed of a complex array of osseous and soft tissue structures. Both common and uncommon clinical entities are encountered in the lateral hip. This article briefly introduces fundamental imaging anatomy and the functional roles of different osseous and soft tissue structures in the lateral aspect of the hip, followed by a discussion of relevant imaging findings of lateral hip pathology. Greater trochanteric pain syndrome is frequently encountered in patients with lateral hip pain and encompasses a spectrum of soft tissue abnormalities including trochanteric and subgluteal bursitis, and tendinopathy or tears of the gluteal tendons. In addition, different types of injuries to the gluteal myotendinous unit and injuries to the indirect head of the rectus femoris, proximal iliotibial band, and the lateral joint capsular ligaments can present with lateral hip pain. Some of the less common soft tissue abnormalities of the lateral hip include Morel-Lavallée lesion and meralgia paresthetica.

Iliopsoas Tendon Tear: Clinical and Imaging Findings in 4 Elderly Patients

Hip pain is a common clinical presentation of elderly patients in the emergency department. We report the clinical and imaging findings in 4 elderly patients with iliopsoas tendon tears who presented at our institution between October 2009 and June 2010. In 2 patients, the imaging diagnosis was significantly delayed. This injury is uncommon, and the clinical presentation in these patients may be misleading. Magnetic resonance is the imaging modality of choice after radiographs to assess these patients, and knowledge of the complex anatomy of the iliopsoas myotendinous unit helps in making the correct diagnosis. With aging of the population, the incidence of iliopsoas tendon tear is likely to increase.

Retraction of Supraspinatus Muscle and Tendon as Predictors of Success of Rotator Cuff Repair

Background: The structural failure rate of rotator cuff repair can exceed 50%. Important predictors for repair failure are preoperative fatty muscle infiltration and myotendinous retraction. Purpose: To quantitatively assess the prognostic value of preoperative retraction of both the supraspinatus muscle and tendon for the outcome of supraspinatus repair. Study Design: Cohort study; Level of evidence, 3. Methods: In 33 shoulders with complete supraspinatus tendon ruptures subjected to arthroscopic repair, magnetic resonance imaging (MRI) scans taken preoperatively and after a mean follow-up of 24 months were studied. The exact position of the lateral extension of the supraspinatus muscle and of the tendon end was evaluated and correlated with the preoperative stage of fatty infiltration (Goutallier) and the failure rate of tendon repair. Results: The mean lengthening of the muscle and tendon end was −3 mm and 4 mm in the failed repairs (n = 19) and 14 mm and 8 mm in the successful repairs (n = 14). If the supraspinatus had preoperative Goutallier stages 2 to 3 and a tendon length of less than 15 mm, the failure rate was 92%, but if the tendon length was greater than 15 mm, the failure rate was only 33%. With Goutallier stages 0 to 1, the corresponding failure rates were 57% and 25%, respectively. Conclusion: Rotator cuff repair lengthens the tendon, even if the repair fails. The possibility to lengthen the myotendinous unit is related to the preoperative length of the tendon. The combination of Goutallier grading and preoperative tendon length appears to be a more powerful predictor for the reparability of a tendon tear than Goutallier grading alone.

The Effects of Unilateral Gastrocsoleus Recession

Gastrocsoleus recession is commonly performed to correct equinus contracture of the ankle that may accompany foot and ankle disease in adults. There is concern that mechanical lengthening of the myotendinous unit causes permanent weakness and disability. This retrospective study reviewed the short-term and long-term objective and subjective results of patients who have had this procedure to determine if it is an appropriate adjunct to corrective foot surgery. Forty patients who had unilateral gastrocsoleus recession either as an isolated procedure or in conjunction with other surgeries were available for evaluation at an average 25.3 (range 6 to 50) months. Followup evaluation included the AOFAS ankle hindfoot score, subjective questionnaire, and physical examination. Preoperative and postoperative ranges of motion were compared. Mechanical strength testing was done using the contralateral extremity as a control. Maximal strength was measured by peak torque using a Cybex device (CYBEX International, Inc., Ronkonkoma, New York). Fatigue resistance was measured by comparing the maximal number of toe raises between the operative and nonoperative sides. Range of motion improved from -3.5 to 15.3 degrees average dorsiflexion. Subjectively, two patients reported pain at the operative site, and one patient reported moderate weakness. The AOFAS score improved from 62.3 to 79.5. Strength testing of plantarflexion peak torque found the operative extremity to be 74% of the contralateral leg at followup. Peak torque improved from an average of 62.6% at 6 to 18 months to 82.2% after 18 months compared to the contralateral extremity. Fatigue resistance improved from 37.6% to 50.3% at 18 months. Two patients reported paresthesias in the sural nerve distribution. Gastrocsoleus recession is an effective procedure to correct equinus contracture either as an isolated procedure or as an adjunct to other foot surgery. While both fatigue resistance and strength decreased initially, both demonstrated improvement over time. Four patients had subjective complaints after the procedure.

The Insertional Footprint of the Rotator Cuff: An Anatomic Study

The purpose of this study was to define the entire rotator cuff footprint and relate it to known, easily identifiable landmarks as a guide for both open and arthroscopic rotator cuff repair. Anatomic: Gross and microscopic. The myotendinous units of the rotator cuff and their insertions onto the humerus were dissected in 20 fresh-frozen cadavers. The separate tendon insertions were identified, and their length and width measured. The character and exact anatomy of the tendons were also noted. The entire insertion was measured and referenced to the articular surface, biceps groove, and bare area of the humerus. In a separate part of the study, 6 cadavers were decalcified and thin-sliced through the supraspinatus tendon insertion. This insertion was evaluated via scanning electron microscopy (SEM). Our findings demonstrated a consistent pattern at the insertion of the rotator cuff. The horseshoe-shaped insertion tapers away from the articular surface in a superior-to-inferior direction. Interdigitation of the muscle units may be noted, particularly between the supraspinatus and the infraspinatus. Average maximum insertional lengths and widths were as follows: subscapularis (SC): 40 x 20 mm; infraspinatus (IS): 29 x 19 mm; supraspinatus (SS): 23 x 16 mm; and teres minor (TM): 29 x 21 mm. The SC inserted on the lesser tuberosity adjacent to the biceps groove at the edge of the articular surface. It tapered away 18 mm at its inferior border. The SS inserted at the articular surface along its entire insertion from the bicipital groove to the top of the bare area. The IS wrapped the posterior border of the SS superiorly at the articular surface and tapered away inferiorly, framing the bare area. SEM microscopy showed the SS to be adherent to the edge of the articular surface medially. As it filled the sulcus, its lateral edge extended over the edge of the greater tuberosity. A consistent pattern was noted at the insertional anatomy of the rotator cuff. This anatomy was related to known, easily identifiable landmarks and may serve as a guide for evaluation of size, location, and propagation patterns of rotator cuff tears, as well as for their repair. Knowledge of the insertional anatomy of the rotator cuff can facilitate grading and repair of rotator cuff tears.

MR Imaging Assessment of the Pectoralis Major Myotendinous Unit

MR imaging is the optimal imaging technique to study the normal and abnormal conditions of the pectoralis major muscle and tendon unit. The purpose of this study was to use MR imaging to provide an anatomic survey of the normal pectoralis major tendon and its insertion and to compare these findings with surgically proven cases of rupture. MR imaging shows the normal pectoralis major myotendinous unit has low signal intensity on both T1- and T2-weighted images. Reliable anatomic landmarks for visualization and examination of injuries to the muscle and myotendinous unit include the quadrilateral space, or the origin of the lateral head of the triceps, as the superior boundary and the deltoid tuberosity as the inferior boundary of the intact tendon of insertion. Failure to visualize a normal insertion within these boundaries should prompt a dedicated search by the radiologist for rupture and retraction of the tendon medially.

PATELLOFEMORAL PAIN SYNDROME IN THE FEMALE ATHLETE

Although PFS will continue to be a therapeutic challenge, the prognosis for most female athletes is good, especially if they are motivated and compliant with their treatment program. Particularly in women, care should be taken to avoid placing too much emphasis on biomechanical variants that may not be clinically significant or correctable because such findings can reinforce a feeling that "nothing can be done." In many cases, muscle dysfunction and repetitive loading of the patellofemoral joint rather than fixed biomechanical factors contribute to the development of PFS. Nonetheless, the importance of a detailed biomechanical assessment on physical examination must not be neglected, particularly in athletes who are not improving with conservative treatment and who may become surgical candidates. A practical initial treatment program for most athletes with nontraumatic PFS begins with relative rest, quadriceps strengthening, and stretching of tight myotendinous units. The introduction of NSAIDs, orthoses, taping, knee sleeves, and more specific rehabilitative exercises should be an individualized decision based on physical findings, past treatment results, and athletic expectations. Surgical referral should be considered in cases of PFS or patellar instability refractory to prolonged maximal nonoperative treatment.

MR imaging of myotendinous strain.

Myotendinous strain predominantly exhibits pathognomonic MR features. Whenever a patient's musculoskeletal symptoms lack temporal correlation with exercise, MR imaging may be valuable in distinguishing strain injury from other disorders of the myotendinous unit. Compared with myotendinous strain, myositis ossificans has variable and nonspecific MR appearances that may simulate neoplasm and require biopsy for diagnosis.

Glenohumeral Motion After Complete Capsular Release

Summary: The range of glenohumeral motion is primarily limited by the joint capsule. If the capsule is contracted, greater restriction in glenohumeral motion is exhibited. Release of a tight capsule has been an effective means of managing refractory stiffness of the glenohumeral joint. The effect of a complete capsular release on glenohumeral kinematics has not been previously studied in a cadaver model. Elevation, rotation, and translation of eight cadaveric glenohumeral preparations were studied before and after complete capsular release. As the intact joint was positioned near the limits of motion, glenohumeral torque rose rapidly with relatively small concomitant increases in elevation and rotational angles. Notable torque, due to tension in the capsule or cuff, ensued only after glenohumeral elevation reached approximately 80% of maximal range. After complete capsular release, maximal elevation increased on average 15%, yet retained definitive endpoints due to residual tension in the rotator cuff. Axial humeral rotation with an intact capsule decreased as maximum elevation approached, especially at elevation angles greater than 60°. Maximum internal rotation was less than external, for all planes except +90°. After complete capsular release, the greatest net gains for external rotation tended to be in the posterior scapular planes, whereas gains for internal rotation tended to be in the anterior scapular planes. Maximal translation in an intact vented capsule was 21 mm, 14 mm, and 15 mm in the anterior, posterior, and inferior directions, respectively. After complete capsular release, translation increased in all positions with maximal anterior, posterior, and inferior translations of 28 mm, 25 mm, and 28 mm, respectively. In general, relative gains in translation were greater in planes posterior to the scapula and at extremes of the range of motion. Although large glenohumeral translations were measured, no preparation could be dislocated before or after complete capsular release. Complete capsular release significantly increased glenohumeral range of motion and translation. The intact rotator cuff myotendinous units serves to limit the range of motion and translation after all capsuloligamentous attachments are rendered incompetent by complete capsular release. Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 15, No 4 (May-June), 1999: pp 408–416