Andrew F. Kuntz

The Effect of Postoperative Passive Motion on Rotator Cuff Healing in a Rat Model

BACKGROUND Surgical repairs of torn rotator cuff tendons frequently fail. Immobilization has been shown to improve tissue mechanical properties in an animal model of rotator cuff repair, and passive motion has been shown to improve joint mechanics in animal models of flexor tendon repair. Our objective was to determine if daily passive motion would improve joint mechanics in comparison with continuous immobilization in a rat rotator cuff repair model. We hypothesized that daily passive motion would result in improved passive shoulder joint mechanics in comparison with continuous immobilization initially and that there would be no differences in passive joint mechanics or insertion site mechanical properties after four weeks of remobilization. METHODS A supraspinatus injury was created and was surgically repaired in sixty-five Sprague-Dawley rats. Rats were separated into three postoperative groups (continuous immobilization, passive motion protocol 1, and passive motion protocol 2) for two weeks before all underwent a remobilization protocol for four weeks. Serial measurements of passive shoulder mechanics (internal and external range of motion and joint stiffness) were made before surgery and at two and six weeks after surgery. After the animals were killed, collagen organization and mechanical properties of the tendon-to-bone insertion site were determined. RESULTS Total range of motion for both passive motion groups (49% and 45% of the pre-injury values) was less than that for the continuous immobilization group (59% of the pre-injury value) at two weeks and remained significantly less following four weeks of remobilization exercise. Joint stiffness at two weeks was increased for both passive motion groups in comparison with the continuous immobilization group. At both two and six weeks after repair, internal range of motion was significantly decreased whereas external range of motion was not. There were no differences between the groups in terms of collagen organization or mechanical properties. CONCLUSIONS In this model, immediate postoperative passive motion was found to be detrimental to passive shoulder mechanics. We speculate that passive motion results in increased scar formation in the subacromial space, thereby resulting in decreased range of motion and increased joint stiffness. Passive motion had no effect on collagen organization or tendon mechanical properties measured six weeks after surgery.

Compartment syndrome in tibial fractures

Objectives: Compartment syndrome is a devastating complication of tibial fractures. The purpose of this study was to investigate the rate of clinically determined compartment syndrome requiring surgical intervention in tibial fractures by anatomical region and to identify the associated patient and injury factors. Design: Retrospective cohort. Setting: University level I trauma center. Patients/Participants: Acute tibial fractures in 414 patients from January 1, 2004 through October 31, 2006. Methods: Tibial fractures in 414 patients met the inclusion and exclusion criteria. The fractures were classified into 3 groups (proximal, diaphyseal, and distal) based on the anatomic location of the fractures (AO/OTA fractures 41, 42, and 43, respectively). To determine the patient and injury factors associated with the development of compartment syndrome in tibial fractures, the following data were obtained: patient age and sex, mechanism of injury, presence of associated fractures, presence of concomitant head/chest/abdominal/pelvic injury, blood pressure upon admission, open versus closed fracture (Gustilo-Anderson classification if open), status of the fibula, and AO/OTA classification of the tibial fracture. Main Outcome Measures: Rate of clinically determined compartment syndrome requiring fasciotomy by anatomical region of the tibia. Results: The rate of compartment syndrome was highest in the diaphyseal group (8.1%, P < 0.05) followed by proximal (1.6%) and distal (1.4%) groups. The diaphyseal group was further analyzed according to patient and injury factors. Patients who developed compartment syndrome were significantly younger (27.5 years ± 11.7 SD versus 39.0 years ± 16.7 SD, P = 0.003, Student t test) than those who did not develop compartment syndrome. The mean arterial pressures upon admission of the patients who developed compartment syndrome were also found to be slightly higher (107 versus 98.5 mm Hg, P = 0.039, Student t test) but not significantly so after Bonferroni adjustment. In multivariate regression analysis, decreasing age remained the only statistically significant independent predictor for the development of compartment syndrome (P = 0.006, regression coefficient = −0.0589) in diaphyseal tibial fractures. Conclusions: Tibial fractures of the diaphysis are more frequently associated with development of compartment syndrome than proximal or distal tibial fractures. More specifically, young patients with diaphyseal fractures are at risk for developing this complication and warrant increased vigilance and suspicion for compartment syndrome. A prospective study with sufficient power is needed to further identify risk factors associated with compartment syndrome in tibial fractures.

Cumulative effects of hypercholesterolemia on tendon biomechanics in a mouse model

High cholesterol represents a significant healthcare problem. Clinical studies have linked hypercholesterolemia to Achilles tendon xanthomas and rotator cuff tears, and research in other systems indicates detrimental effects of high cholesterol; however, understanding of its impact on tendon properties and healing is limited. We hypothesized that tendons from aging hypercholesterolemic (APOE) mice would exhibit inferior baseline and healing mechanical properties compared to controls, while younger, but mature mice would be no different. Surprisingly, tensile testing of patellar tendons from 14‐week‐old APOE mice receiving a unilateral full‐thickness central defect resulted in normalized (injured:sham) cross‐sectional areas closer to baseline (p = 0.02) compared to controls. Uninjured data from 10‐month‐old APOE mice showed a decrease in elastic modulus (p = 0.02), indicating a detrimental effect of hypercholesterolemia on tendon properties in this model. These results could benefit patients through knowledge that high cholesterol could increase the likelihood of tendon tears. Furthermore, knowledge that tendon tears are indicative of high cholesterol could provide orthopedic clinicians with an additional preventive treatment opportunity for patients with undiagnosed hypercholesterolemia.

Development and evaluation of multiple tendon injury models in the mouse

The mouse has proven to be an advantageous animal model system in basic science research focused on aiding in development and evaluation of potential treatments; however, the small size of mouse tendons makes consistent and reproducible injury models and subsequent biomechanical evaluation challenging for studying tendon healing. In this study, we investigated the feasibility and reproducibility of multiple mouse tendon injury models. Our hypothesis was that incisional (using a blade) and excisional (using a biopsy punch) injuries would result in consistent differences in tendon material properties. At 16 weeks of age, 17 C57BL/6 mice underwent surgery to create defects in the flexor digitorum longus, Achilles, or patellar tendon. Each animal received 1-2 full-thickness, central-width incisional or excisional injuries per limb; at least one tendon per limb remained uninjured. The injuries were distributed such that each tendon type had comparable numbers of uninjured, incisionally injured, and excisionally injured specimens. Three weeks after injury, all animals were euthanized and tendons were harvested for mechanical testing. As hypothesized, differences were detected for all three different tendon types at three weeks post-injury. While all models created injuries that produced predictable outcomes, the patellar tendon model was the most consistent in terms of number and size of significant differences in injured tendons compared to native properties, as well as in the overall variance in the data. This finding provides support for its use in fundamental tendon healing studies; however, future work may use any of these models, based on their appropriateness for the specific question under study.

Scapular Dyskinesis is Detrimental to Shoulder Tendon Properties and Joint Mechanics in a Rat Model

Shoulder tendon injuries are frequently seen in the presence of abnormal scapular motion, termed scapular dyskinesis. The cause and effect relationship between scapular dyskinesis and shoulder injury has not been directly defined. We developed and used an animal model to examine the initiation and progression of pathological changes in the rotator cuff and biceps tendon. Sixty male Sprague–Dawley rats were randomized into two groups: nerve transection (to induce scapular dyskinesis, SD) or sham nerve transection (control). The animals were euthanized 4 and 8 weeks after surgery. Shoulder function and passive joint mechanics were evaluated over time. Tendon mechanical, histological, organizational, and compositional properties were evaluated at both time points. Gross observation demonstrated alterations in scapular motion, consistent with scapular “winging.” Shoulder function, passive internal range of motion, and tendon mechanical properties were significantly altered. Histology results, consistent with tendon pathology (rounded cell shape and increased cell density), were observed, and protein expression of collagen III and decorin was altered. This study presents a new model of scapular dyskinesis that can rigorously evaluate cause and effect relationships in a controlled manner. Our results identify scapular dyskinesis as a causative mechanical mechanism for shoulder tendon pathology.

Twenty‐five years of tendon and ligament research

Twenty‐five years ago, the Journal of Orthopaedic Research published its first volume, which included five articles covering topics in tendon and ligament research. Since then, the body of tendon and ligament research has continued to increase exponentially. This review summarizes major advancements in tendon and ligament research since the initial publication of this journal. The purpose of this article is not to provide an in‐depth review of all of tendon and ligament research, but instead to provide a concise literature review of some of the major and recurring areas of research. The general topics covered over the last 25 years include tissue properties, tendinopathy, healing, and engineered scaffolds.

Effect of anterior supraspinatus tendon partial-thickness tears on infraspinatus tendon strain through a range of joint rotation angles

BACKGROUND Rotator cuff tears are common shoulder problems whose propagation is difficult to predict because of the structural and mechanical inhomogeneity of the supraspinatus tendon. We have previously shown that the supraspinatus and infraspinatus tendons interact mechanically when the supraspinatus tendon is intact or exhibits a full-thickness tear, so that an increase in supraspinatus tendon strain is paralleled by an increase in infraspinatus tendon strain. Such interaction is critical and suggests that an increase in infraspinatus tendon strain that accompanies an increase in supraspinatus tendon strain may shield the supraspinatus tendon from further injury, but increase the risk of injury to the infraspinatus tendon. In this study, the mechanical interactions between the supraspinatus and infraspinatus tendons were evaluated for the commonly occurring supraspinatus tendon partial-thickness tears through a range of rotation angles. METHODS For each joint rotation and supraspinatus tendon tear size evaluated, the supraspinatus tendon was loaded, and images corresponding to 5 N, 30 N, 60 N, and 90 N of supraspinatus tendon load were isolated for the speckle painted supraspinatus and infraspinatus tendons. A region of interest outlining the insertion site was isolated and displacements between the 5 N loaded image and each of the others were measured, from which normalized average principal strains were quantified in both tendons. RESULTS The observed effect on infraspinatus tendon strain paralleled that observed on strain in the supraspinatus tendon. Introducing a supraspinatus tendon partial-thickness tear and increasing load caused an increase in normalized average maximum and a decrease in normalized average minimum principal strain in the infraspinatus tendon. Increasing rotation angle from internal to external rotation caused a general decrease in normalized average maximum and increase in normalized average minimum principal strain in both tendons. CONCLUSION The supraspinatus and infraspinatus tendons mechanically interact for the intact and partially torn supraspinatus tendons for neutral and rotated glenohumeral joint.

Arthroscopic subscapularis repair.

&NA; As the largest and most powerful rotator cuff muscle, the subscapularis plays a critical role in proper shoulder function. The diagnosis of subscapularis tears is made based on history and physical examination and confirmed with imaging studies. Historically, subscapularis tears have been addressed in an open fashion. Recent literature has demonstrated successful all‐arthroscopic repair of isolated subscapularis tears and anterosuperior rotator cuff tears. Successful arthroscopic treatment follows several critical steps: patient positioning, portal placement, obtaining adequate visualization and working space, identifying and mobilizing the subscapularis tendon, preparation of the tendon edge and lesser tuberosity, appropriate anchor placement, suture passage, and finally, secure knot‐tying and fixation. Excellent functional and clinical outcomes following these steps have been demonstrated by various investigators. Additional research is needed, however, because direct comparison between all‐arthroscopic and open subscapularis repair is limited, and neither technique has proved to be superior.

Effect of glenohumeral abduction angle on the mechanical interaction between the supraspinatus and infraspinatus tendons for the intact, partial-thickness torn, and repaired supraspinatus tendon conditions

Rotator cuff tears are difficult to manage because of the structural and mechanical inhomogeneity of the supraspinatus tendon. Previously, we showed that with the arm at the side, the supraspinatus and infraspinatus tendons mechanically interact such that conditions that increase supraspinatus tendon strain, such as load or full‐thickness tears, also increase infraspinatus tendon strain. This suggests that the infraspinatus tendon may shield the supraspinatus tendon from further injury while becoming at increased risk of injury itself. In this study, the effect of glenohumeral abduction angle on the interaction between the two tendons was evaluated for supraspinatus tendon partial‐thickness tears and two repair techniques. Principal strains were quantified in both tendons for 0°, 30°, and 60° of glenohumeral abduction. Results showed that interaction between the two tendons is interrupted by an increase in abduction angle for all supraspinatus tendon conditions evaluated. Infraspinatus tendon strain was lower at 30° and 60° than at 0° abduction angle. In conclusion, interaction between the supraspinatus and infraspinatus tendons is interrupted with increase in abduction angle. Additionally, 30° abduction should be further evaluated for management of rotator cuff tears and repairs as it is the angle at which both supraspinatus and infraspinatus tendon strain is decreased.

Effect of overuse-induced tendinopathy on tendon healing in a rat supraspinatus repair model.

Supraspinatus tears often result in the setting of chronic tendinopathy. However, the typical repair model utilizes an acute injury. In recognition of that distinction, our laboratory developed an overuse animal model; however it is unclear whether induced overuse is necessary in the repair model. We studied the repair properties of overuse‐induced tendons compared to normal tendons. We hypothesized that histological and mechanical properties would not be altered between the overuse‐induced and normal tendons 1 and 4 weeks after repair. Thirty‐one adult male Sprague‐Dawley rats were subjected to either overuse or cage activity for 4 weeks prior to bilateral supraspinatus tendon repair surgery. Rats were sacrificed at 1 and 4 weeks post‐surgery and evaluated for histology and mechanics. Results at 1 week showed no clear histologic changes, but increased inflammatory protein expression in overuse tendons. At 4 weeks, percent relaxation was slightly increased in the overuse group. No other alterations in mechanics or histology were observed. Our results suggest that the effects of the surgical injury overshadow the changes evoked by overuse. Because clinically relevant mechanical parameters were not altered in the overuse group, we conclude that when examining tendons 4 weeks after repair in the classic rat supraspinatus model, inducing overuse prior to surgery is likely to be unnecessary.