Christopher J. Tuohy

Complex regional pain syndrome after hand surgery.

Complex regional pain syndrome (CRPS) after an emergent or elective upper extremity surgery may complicate recovery, delay return to work, diminish health-related quality of life, and increase the likelihood of poor outcomes and/or litigation. CRPS after hand surgery is not uncommon and may complicate postoperative care. Early diagnosis and treatment of CRPS is critical for optimal patient outcomes. This article discusses the diagnosis, physiology, and management of postsurgical CRPS that occurs after hand surgery.

Evaluation of in vivo rotator cuff muscle function after acute and chronic detachment of the supraspinatus tendon: an experimental study in an animal model.

BACKGROUND Surgical repair of large chronic rotator cuff tears can be technically demanding because it requires manipulation of a muscle-tendon unit that is scarred, retracted, and stiffer than normal, all of which contribute to increased tension at the repair site. The purpose of the present study was to characterize the in vivo rotator cuff muscle-tendon unit function after acute and chronic injury at surgically relevant preload tensions. METHODS Sixty-two Sprague-Dawley rats were divided into a healthy, uninjured (control) group (n = 22), an acute injury group (n = 20), and a chronic injury group (n = 20) and underwent in vivo muscle force testing and electromyographic testing of the supraspinatus muscle-tendon unit at various preload tensions. RESULTS Preload tension affected the maximum supraspinatus muscle contractile force in all groups (p < 0.05). At the peak tension required to repair an acute tear, there was a 28% to 30% reduction in maximum tetanic contraction amplitude in all groups (p < 0.05). At the peak tension required to repair a chronic tear, there was a 40% to 53% reduction in maximal tetanic contraction amplitude in all groups (p < 0.05). The uninjured (control) group showed increased muscle endurance (p < 0.05) in comparison with the acute injury and chronic injury groups at all preload tensions. The chronic injury group showed reduced compound motor action potential amplitude (p < 0.05). CONCLUSIONS Both the acute and chronic injury groups demonstrated functional impairment related to increasing preload tensions. Higher repair tensions, associated with the chronic injury setting, resulted in greater functional impairment. The present study also demonstrates an association between increased time from rotator cuff tendon injury and impaired in vivo rotator cuff muscle electromyographic findings.

Postural dependence of passive tension in the supraspinatus following rotator cuff repair: A simulation analysis☆

BACKGROUND Despite surgical advances, repair of rotator cuff tears is associated with 20-70% incidence of recurrent tearing. The tension required to repair the torn tendon influences surgical outcomes and may be dependent on the gap length from torn tendon that must be spanned by the repair. Detailed understanding of forces throughout the range of motion (ROM) may allow surgeons to make evidence-based recommendations for post-operative care. METHODS We used a computational shoulder model to assess passive tension and total moment-generating capacity in supraspinatus for repairs of gaps up to 3 cm throughout the shoulder (ROM). FINDINGS In 60° abduction, increased gap length from 0.5 cm to 3 cm caused increases in passive force from 3N to 58 N, consistent with those seen during clinical repair. For reduced abduction, passive forces increased substantially. For a 0.5 cm gap, tension throughout the ROM (elevation, plane of elevation, and rotation) is within reasonable limits, but larger gaps are associated with tensions that markedly exceed reported pull-out strength of sutures and anchors. Peak moment for a large 3 cm gap length was 5.09 Nm, a 53% reduction in moment-generating capacity compared to uninjured supraspinatus. INTERPRETATION We conclude that shoulder posture is an important determinant of passive forces during rotator cuff repair surgery. Choosing postures that reduce forces intraoperatively to permit repair of larger gaps may lead to failure postoperatively when the shoulder is mobilized. For larger defects, loss of strength in supraspinatus may be substantial following repair even if retear is prevented.

Advanced Age Diminishes Tendon-to-Bone Healing in a Rat Model of Rotator Cuff Repair

Background: Advanced patient age is associated with recurrent tearing and failure of rotator cuff repairs clinically; however, basic science studies have not evaluated the influence of aging on tendon-to-bone healing after rotator cuff repair in an animal model. Hypothesis/Purpose: This study examined the effect of aging on tendon-to-bone healing in an established rat model of rotator cuff repair using the aged animal colony from the National Institute on Aging of the National Institutes of Health. The authors hypothesized that normal aging decreases biomechanical strength and histologic organization at the tendon-to-bone junction after acute repair. Study Design: Controlled laboratory study. Methods: In 56 F344xBN rats, 28 old and 28 young (24 and 8 months of age, respectively), the supraspinatus tendon was transected and repaired. At 2 or 8 weeks after surgery, shoulder specimens underwent biomechanical testing to compare load-to-failure and load-relaxation response between age groups. Histologic sections of the tendon-to-bone interface were assessed with hematoxylin and eosin staining, and collagen fiber organization was assessed by semiquantitative analysis of picrosirius red birefringence under polarized light. Results: Peak failure load was similar between young and old animals at 2 weeks after repair (31% vs 26% of age-matched uninjured controls, respectively; P > .05) but significantly higher in young animals compared with old animals 8 weeks after repair (86% vs 65% of age-matched uninjured controls, respectively; P < .01). Eight weeks after repair, fibroblasts appeared more organized and uniformly aligned in young animals on hematoxylin and eosin slides compared with old animals. Collagen birefringence analysis of the tendon-to-bone junction demonstrated that young animals had increased collagen fiber organization and similar histologic structure compared with age-matched controls (53.7 ± 2.4 gray scales; P > .05). In contrast, old animals had decreased collagen fiber organization and altered structure compared with age-matched controls (49.8 ± 3.1 gray scales; P < .01). Discussion: In a rat model of aging, old animals demonstrated diminished tendon-to-bone healing after rotator cuff injury and repair. Old animals had significantly decreased failure strength and collagen fiber organization at the tendon-to-bone junction compared with young animals. This study implies that animal age may need to be considered in future studies of rotator cuff repair in animal models. Clinical Relevance: With increasing age and activity level of the population, the incidence of rotator cuff tears is predicted to rise. Despite advances in rotator cuff repair technique, the retear rate remains specifically high in elderly patients. The findings of this research suggest that aging negatively influences tendon-to-bone healing after rotator cuff repair in a validated animal model.

Rotator cuff injuries in professional and recreational athletes.

Professional and recreational athletes involved in contact sports and sports with repetitive overhead motion are at increased risk for rotator cuff tears. Shoulder anatomy, pathology, and biomechanics place unique stress on the rotator cuff tendons during sports activity. Athletes demand effective treatment to quickly return to elite competition. A PubMed search assessed treatment options providing expedited recovery time and return to competition. Twelve of 231 articles fit the objective criteria; 90.5% of professional contact athletes, 40% of professional overhead athletes, and 83.3% of recreational athletes fully recovered following rotator cuff tear surgical repair. Prompt surgical treatment for full-thickness rotator cuff tears may be appropriate for contact athletes and recreational overhead athletes. Although professional overhead athletes have low recovery rates, surgical repair of full-thickness rotator cuff tears may still be indicated. The authors propose a treatment algorithm based on the limited literature (mainly level 4 and 5 evidence).

Age-related changes affect rat rotator cuff muscle function

BACKGROUND The influence of age on rotator cuff function and muscle structure remains poorly understood. We hypothesize that normal aging influences rotator cuff function, muscle structure, and regulatory protein expression in an established rat model of aging. METHODS Seventeen rats were obtained from the National Institute on Aging. The supraspinatus muscles in 11 middle-aged (12 months old) and 6 old (28 months old) rats were studied for age-related changes in rotator cuff neuromuscular function by in vivo muscle force testing and electromyography (EMG). Changes in muscle structure and molecular changes were assessed with quantitative immunohistochemistry for myogenic determination factor 1 (MyoD) and myogenic factor 5 (Myf5) expression. RESULTS Old animals revealed significantly decreased peak tetanic muscle force at 0.5 N and 0.7 N preload tension (P < .05). The age of the animal accounted for 20.9% of variance and significantly influenced muscle force (P = .026). Preload tension significantly influenced muscle force production (P < .001) and accounted for 12.7% of total variance. There was regional heterogeneity in maximal compound motor action potential (CMAP) amplitude in the supraspinatus muscle; the proximal portion had a significantly higher CMAP than the middle and distal portions (P < .05). The expression of muscle regulatory factors MyoD and Myf5 was significantly decreased in old animals compared with middle-aged animals (P < .05). CONCLUSIONS The normal aging process in this rat model significantly influenced contractile strength of the supraspinatus muscle and led to decreased expression of muscle regulatory factors. High preload tensions led to a significant decrease in force production in both middle-aged and old animals.

Chemical Denervation with Botulinum Neurotoxin A Improves the Surgical Manipulation of the Muscle–Tendon Unit: An Experimental Study in an Animal Model

PURPOSE The chemical denervation that results from botulinum neurotoxin A (BoNT-A) causes a temporary, reversible paresis that can result in easier surgical manipulation of the muscle-tendon unit in the context of tendon rupture and repair. The purpose of the study was to determine whether BoNT-A injections can be used to temporarily and reversibly modulate active and passive skeletal muscle properties. METHODS Male CD1 mice weighing 40-50 g were divided into a 1-week postinjection group (n = 13: n = 5 saline and n = 8 BoNT-A) and a 2-week postinjection group (n = 17: n = 7 saline and n = 10 BoNT-A). The animals had in vivo muscle force testing and in vivo biomechanical evaluation. RESULTS There was a substantial decline in the maximal single twitch amplitude (p < .05) and tetanic amplitude (p < .05) at one week and at 2 weeks after BoNT-A injection, when compared to saline-injected controls. BoNT-A injection significantly reduced the peak passive properties of the muscle-tendon unit as a function of displacement at one week (p < .05). Specifically, the stiffness of the BoNT-A injected muscle-tendon unit was 0.417 N/mm compared to the control saline injected group, which was 0.634 N/mm, a 35% reduction in stiffness (p < .05). CONCLUSIONS Presurgical treatment with BoNT-A might improve the surgical manipulation of the muscle-tendon unit, thus improving surgical outcomes. The results implicate neural tone as a substantial contributor to the passive repair tension of the muscle-tendon unit. The modulation of neural tone through temporary, reversible paresis is a novel approach that might improve intraoperative and postoperative passive muscle properties, allowing for progressive rehabilitation while protecting the surgical repair site.

The science of rotator cuff tears: translating animal models to clinical recommendations using simulation analysis

PurposeThe purpose of this article is to review basic science studies using various animal models for rotator cuff research and to describe structural, biomechanical, and functional changes to muscle following rotator cuff tears. The use of computational simulations to translate the findings from animal models to human scale is further detailed.MethodsA comprehensive review was performed of the basic science literature describing the use of animal models and simulation analysis to examine muscle function following rotator cuff injury and repair in the ageing population.ResultsThe findings from various studies of rotator cuff pathology emphasize the importance of preventing permanent muscular changes with detrimental results. In vivo muscle function, electromyography, and passive muscle–tendon unit properties were studied before and after supraspinatus tenotomy in a rodent rotator cuff injury model (acute vs chronic). Then, a series of simulation experiments were conducted using a validated computational human musculoskeletal shoulder model to assess both passive and active tension of rotator cuff repairs based on surgical positioning.ConclusionOutcomes of rotator cuff repair may be improved by earlier surgical intervention, with lower surgical repair tensions and fewer electromyographic neuromuscular changes. An integrated approach of animal experiments, computer simulation analyses, and clinical studies may allow us to gain a fundamental understanding of the underlying pathology and interpret the results for clinical translation.

The effects of a rotator cuff tear on activities of daily living in older adults: A kinematic analysis

Rotator cuff tears (RCT) in older individuals may compound age-associated physiological changes and impact their ability to perform daily functional tasks. Our objective was to quantify thoracohumeral kinematics for functional tasks in 18 older adults (mean age=63.3±2.2), and compare findings from nine with a RCT to nine matched controls. Motion capture was used to record kinematics for 7 tasks (axilla wash, forward reach, functional pull, hair comb, perineal care, upward reach to 90°, upward reach to 105°) spanning the upper limb workspace. Maximum and minimum joint angles and motion excursion for the three thoracohumeral degrees of freedom (elevation plane, elevation, axial rotation) were identified for each task and compared between groups. The RCT group used greater minimum elevation angles for axilla wash and functional pull (p≤0.0124) and a smaller motion excursion for functional pull (p=0.0032) compared to the control group. The RCT group also used a more internally rotated maximum axial rotation angle than controls for functional reach, functional pull, hair comb, and upward reach to 105° (p≤0.0494). The most differences between groups were observed for axial rotation, with the RCT group using greater internal rotation to complete functional tasks, and significant differences between groups were identified for all three thoracohumeral degrees of freedom for functional pull. We conclude that older adults with RCT used more internal rotation to perform functional tasks than controls. The kinematic differences identified in this study may have consequences for progression of shoulder damage and further functional impairment in older adults with RCT.

A randomized trial of diagnostic ultrasound to improve outcomes in focal neuropathies.

Introduction: Neuromuscular ultrasound is valid, reliable, and accurate, but it is not known whether combining it with electrodiagnostic studies leads to better outcomes in individuals with focal neuropathies. Methods: One hundred twenty individuals with focal neuropathy, based on history, examination, and electrodiagnosis, were enrolled in this study. All patients underwent neuromuscular ultrasound and were randomized to either have their ultrasound results sent to the referring physician or not have them sent. Outcomes were assessed at 6 months by evaluators blinded to group assignment. Results: The Overall Disability Sum Score and 7 of 8 domains of the Medical Outcomes Study 36‐item Short‐Form Health Survey (SF‐36) showed more improvement in the “report sent” group, although only the general health perception domain was significant (P = 0.005). Conclusions: Most 6‐month outcomes did not reach statistical significance between the 2 groups. However, the “report sent” group had trends toward better outcomes, with significance being reached in the general health perception domain of the SF‐36. Muscle Nerve 52: 746–753, 2015