Where tendons and ligaments meet bone: attachment sites ('entheses') in relation to exercise and/or mechanical load

Adductor-related groin pain in recreational athletes: role of the adductor enthesis, magnetic resonance imaging, and entheseal pubic cleft injections

BACKGROUND

Adductor dysfunction can cause groin pain in athletes and may emanate from the adductor enthesis. Adductor enthesopathy may be visualized with magnetic resonance imaging and may be treated with entheseal pubic cleft injections. We have previously reported that pubic cleft injections can provide predictable pain relief at one year in competitive athletes who have no evidence of enthesopathy on magnetic resonance imaging and immediate relief only in patients with findings of enthesopathy on magnetic resonance imaging. In this follow-up study, we attempted to determine if the same holds true for recreational athletes.

METHODS

We reviewed a consecutive case series of twenty-eight recreational athletes who had presented to our sports medicine clinic with groin pain secondary to adductor longus dysfunction. A period of conservative treatment had failed for all of these athletes. The adductor longus origin was assessed with magnetic resonance imaging for the presence or absence of enthesopathy. All patients were treated with a single pubic cleft injection of a local anesthetic and corticosteroid into the adductor enthesis. The patients were assessed for recurrence of symptoms at one year after treatment.

RESULTS

On clinical reassessment five minutes after the injection, all twenty-eight athletes reported resolution of the groin pain. Fifteen patients (Group 1) had no evidence of enthesopathy on magnetic resonance imaging, and thirteen patients (Group 2) had findings of enthesopathy on magnetic resonance imaging. At one year after the injection, five of the fifteen patients in Group 1 had experienced a recurrence; these recurrences were noted at a mean of fourteen weeks (range, seven to twenty weeks) after the injection. Four of the thirteen patients in Group 2 had experienced a recurrence of the symptoms at one year, and these recurrences were noted at a mean of eight weeks (range, two to nineteen weeks) after the injection. Overall, nineteen (68%) of the twenty-eight athletes had a good result following the injection. Of the remaining nine athletes, two were treated successfully with repeat injection; therefore, overall, twenty-one (75%) of the twenty-eight athletes had a good result after entheseal pubic cleft injection.

CONCLUSIONS

Most recreational athletes with adductor enthesopathy have pain relief at one year after entheseal pubic cleft injection, regardless of the findings on magnetic resonance imaging. There were similarities between this group of recreational athletes and the competitive athletes in our previous study, in that the adductor enthesis was the source of pain and entheseal pubic cleft injection was a valuable treatment option. The main difference was that, in this group of recreational athletes, magnetic resonance imaging evidence of adductor enthesopathy did not correlate with the outcome of the injection.

Engineering the bone-ligament interface using polyethylene glycol diacrylate incorporated with hydroxyapatite

Ligaments and tendons have previously been tissue engineered. However, without the bone attachment, implantation of a tissue-engineered ligament would require it to be sutured to the remnant of the injured native tissue. Due to slow repair and remodeling, this would result in a chronically weak tissue that may never return to preinjury function. In contrast, orthopaedic autograft reconstruction of the ligament often uses a bone-to-bone technique for optimal repair. Since bone-to-bone repairs heal better than other methods, implantation of an artificial ligament should also occur from bone-to-bone. The aim of this study was to investigate the use of a poly(ethylene glycol) diacrylate (PEGDA) hydrogel incorporated with hydroxyapatite (HA) and the cell-adhesion peptide RGD (Arg-Gly-Asp) as a material for creating an in vitro tissue interface to engineer intact ligaments (i.e., bone-ligament-bone). Incorporation of HA into PEG hydrogels reduced the swelling ratio but increased mechanical strength and stiffness of the hydrogels. Further, HA addition increased the capacity for cell growth and interface formation. RGD incorporation increased the swelling ratio but decreased mechanical strength and stiffness of the material. Optimum levels of cell attachment were met using a combination of both HA and RGD, but this material had no better mechanical properties than PEG alone. Although adherence of the hydrogels containing HA was achieved, failure occurs at about 4 days with 5% HA. Increasing the proportion of HA improved interface formation; however, with high levels of HA, the PEG HA composite became brittle. This data suggests that HA, by itself or with other materials, might be well suited for engineering the ligament-bone interface.

Survey of the enthesopathy of X-linked hypophosphatemia and its characterization in Hyp mice

X-linked hypophosphatemia (XLH) is characterized by rickets and osteomalacia as a result of an inactivating mutation of the PHEX (phosphate-regulating gene with homology to endopeptidases on the X chromosome) gene. PHEX encodes an endopeptidase that, when inactivated, results in elevated circulating levels of FGF-23, a novel phosphate-regulating hormone (a phosphatonin), thereby resulting in increased phosphate excretion and impaired bone mineralization. A generalized and severe mineralizing enthesopathy in patients with XLH was first reported in 1985; we likewise report a survey in which we found evidence of enthesopathy in fibrocartilaginous insertion sites, as well as osteophyte formation, in the majority of patients. Nonetheless, there has been very little focus on the progression and pathogenesis underlying the paradoxical heterotopic calcification of tendon and ligament insertion sites. Such studies have been hampered by lack of a model of mineralizing enthesopathy. We therefore characterized the involvement of the most frequently targeted fibrocartilaginous tendon insertion sites in Hyp mice, a murine model of the XLH mutation that phenocopies the human syndrome in every detail including hypophosphatemia and elevated FGF-23. Histological examination of the affected entheses revealed that mineralizing insertion sites, while thought to involve bone spur formation, were not due to bone-forming osteoblasts but instead to a significant expansion of mineralizing fibrocartilage. Our finding that enthesis fibrocartilage cells specifically express fibroblast growth factor receptor 3 (FGFR3)/Klotho suggests that the high circulating levels of FGF-23, characteristic of XLH and Hyp mice, may be part of the biochemical milieu that underlies the expansion of mineralizing enthesis fibrocartilage.

Management of tendinopathy

Overuse disorders of tendons, or tendinopathies, present a challenge to sports physicians, surgeons, and other health care professionals dealing with athletes. The Achilles, patellar, and supraspinatus tendons are particularly vulnerable to injury and often difficult to manage successfully. Inflammation was believed central to the pathologic process, but histopathologic evidence has confirmed the failed healing response nature of these conditions. Excessive or inappropriate loading of the musculotendinous unit is believed to be central to the disease process, although the exact mechanism by which this occurs remains uncertain. Additionally, the location of the lesion (for example, the midtendon or osteotendinous junction) has become increasingly recognized as influencing both the pathologic process and subsequent management. The mechanical, vascular, neural, and other theories that seek to explain the pathologic process are explored in this article. Recent developments in the nonoperative management of chronic tendon disorders are reviewed, as is the rationale for surgical intervention. Recent surgical advances, including minimally invasive tendon surgery, are reviewed. Potential future management strategies, such as stem cell therapy, growth factor treatment, and gene transfer, are also discussed.

Scientific bases and clinical utilisation of the calf-raise test

BACKGROUND

Athletes commonly sustain injuries to the triceps surae muscle-tendon unit. The calf-raise test (CRT) is frequently employed in sports medicine for the detection and monitoring of such injuries. However, despite being widely-used, a recent systematic review found no universal consensus relating to the test's purpose, parameters, and standard protocols.

OBJECTIVES

The purpose of this paper is to provide a clinical perspective on the anatomo-physiological bases underpinning the CRT and to discuss the utilisation of the test in relation to the structure and function of the triceps surae muscle-tendon unit.

DESIGN

Structured narrative review.

METHODS

Nine electronic databases were searched using keywords and MESH headings related to the CRT and the triceps surae muscle-tendon unit anatomy and physiology. A hand-search of reference lists and relevant journals and textbooks complemented the electronic search.

SUMMARY

There is evidence supporting the clinical use of the CRT to assess soleus and gastrocnemius, their shared aponeurosis, the Achilles tendon, and the combined triceps surae muscle-tendon unit. However, employing the same clinical test to assess all these structures and their associated functions remains challenging.

CONCLUSIONS

Further refinement of the CRT for the triceps surae muscle-tendon unit is needed. This is vital to support best practice utilisation, standardisation, and interpretation of the CRT in sports medicine.

Nanoindentation of the insertional zones of human meniscal attachments into underlying bone

The fibrocartilagenous knee menisci are situated between the femoral condyles and tibia plateau and are primarily anchored to the tibia by means of four attachments at the anterior and posterior horns. Strong fixation of meniscal attachments to the tibial plateau provide resistance to extruding forces of the meniscal body, allowing the menisci to assist in load transmission from the femur to the tibia. Clinically, tears and ruptures of the meniscal attachments and insertion to bone are rare. While it has been suggested that the success of a meniscal replacement is dependent on several factors, one of which is the secure fixation and firm attachment of the replacement to the tibial plateau, little is known about the material properties of meniscal attachments and the transition in material properties from the meniscus to subchondral bone. The objective of this study was to use nanoindentation to investigate the transition from meniscal attachment into underlying subchondral bone through uncalcified and calcified fibrocartilage. Nanoindentation tests were performed on both the anterior and posterior meniscal insertions to measure the instantaneous elastic modulus and elastic modulus at infinite time. The elastic moduli were found to increase in a bi-linear fashion from the external ligamentous attachment to the subchondral bone. The elastic moduli for the anterior attachments were consistently larger than those for the matching posterior attachments at similar indentation locations. These results show that there is a gradient of stiffness from the superficial zones of the insertion close to the ligamentous attachment into the deeper zones of the bone. This information will be useful in the continued development of successful meniscal replacements and understanding of fixation of the replacements to the tibial plateau.

Ultrasound imaging of the patellar tendon attachment to the tibia during puberty: a 12-month follow-up in tennis players

This longitudinal study investigated the ultrasound appearance of the patellar tendon attachment to the tibia throughout puberty in young tennis players with and without Osgood-Schlatter disease (OSD). Twenty-eight competitive players (17 boys), aged 10.6-15.3 years, had bilateral ultrasound imaging of the patellar tendon attachment to the tibia at baseline and 1 year later. On each occasion, anthropometric measurements, pubertal status and injury history were recorded. Ultrasound appearance of the patellar tendon attachment was categorized into three stages: cartilage attachment, insertional cartilage and mature attachment. Stage 1 appearance, a large anechoic region with or without ossicles and irregularity of the apophysis that are classically associated with OSD, was found in eight players, seven of them were pain free. A majority (62%) of the patellar tendons in stage 1 at baseline progressed toward stage 2 or stage 3 1 year later. Likewise the patellar tendon attachment in most athletes with cartilage insertion showed progression to a mature enthesis over 1 year. The imaging appearance that is classically interpreted as OSD was common in asymptomatic knees. This ultrasonographic description of the patellar tendon attachment to the tibia during growth provides a reference for the assessment of bone tendon attachments in adolescents.

Axial and appendicular skeletal transformations, ligament alterations, and motor neuron loss in Hoxc10 mutants

Vertebrate Hox genes regulate many aspects of embryonic body plan development and patterning. In particular, Hox genes have been shown to regulate regional patterning of the axial and appendicular skeleton and of the central nervous system. We have identified patterning defects resulting from the targeted mutation of Hoxc10, a member of the Hox10 paralogous family. Hoxc10 mutant mice have skeletal transformations in thoracic, lumbar, and sacral vertebrae and in the pelvis, along with alterations in the bones and ligaments of the hindlimbs. These results suggest that Hoxc10, along with other members of the Hox10 paralogous gene family, regulates vertebral identity at the transition from thoracic to lumbar and lumbar to sacral regions. Our results also suggest a general role for Hoxc10 in regulating chondrogenesis and osteogenesis in the hindlimb, along with a specific role in shaping femoral architecture. In addition, mutant mice have a reduction in lumbar motor neurons and a change in locomotor behavior. These results suggest a role for Hoxc10 in generating or maintaining the normal complement of lumbar motor neurons.

Repair process after fibrocartilaginous enthesis drilling: histological study in a rabbit model

BACKGROUND

Disorders of the enthesis are often a consequence of sports injuries. However, there is uncertainty regarding the process of mechanical stress-related injuries at the enthesis and the subsequent repair process of the injured tissues. To elucidate the repair process of the fibrocartilaginous enthesis, we studied the repair of injured fibrocartilaginous enthesis and the morphological characteristics of the repaired tissue.

METHODS

We drilled 0.5-mm holes in the right tibial insertion of the patellar tendon of Japanese white rabbits, with their own left sides serving as controls. Specimens harvested at 1, 2, 4, 6, 8, and 12 weeks were examined histologically. Morphologically, the ratios of calcified fibrocartilage-bone interface lengths to enthesial lengths were compared between the control and surgical groups.

RESULTS

Repair initiation was observed in the deep bone layer at 1 week, with remarkable progress at 2 weeks. Repair at the enthesis and neoosteogenesis in deep bone layers were detected at 4 weeks, and the drill hole disappeared at 6 weeks. The tendon was partially invaded by fibrocartilage-covered chondroid bone at 8 weeks, and regenerated fibrocartilaginous enthesis and increased calcified fibrocartilage-bone interface irregularity was identified at 12 weeks. The ratios of calcified fibrocartilage-bone interface lengths to enthesial lengths were significantly greater in the surgical group than in the control group.

CONCLUSIONS

Repair progressed from bone to fibrocartilage and ended at fibrous tissue. Cancellous bone disruption triggered repair in all layers. Removal of the subchondral plate enabled infiltration of nutrients via blood vessels, with the underlying bone acting as a scaffold for the regenerating fibrocartilage.

The enthesis organ concept and its relevance to the spondyloarthropathies

A characteristic feature of the spondyloarthropathies is inflammation at tendon or ligament attachment sites. This has traditionally been viewed as a focal abnormality, even though the inflammatory reaction intrinsic to enthesitis may be quite extensive. We argue that the diffuse nature of the pathology is best understood in the context of an 'enthesis organ concept'. This highlights the fact that stress concentration at an insertion site involves not only the enthesis itself, but neighbouring tissues as well. The archetypal enthesis organ is that of the Achilles tendon where intermittent contact between tendon and bone immediately proximal to the enthesis leads to the formation of fibrocartilages on the deep surface of the tendon and on the opposing calcaneal tuberosity, but similar functional modifications are widespread throughout the skeleton. Many entheses have bursae and fat near the insertion site and both of these serve to promote frictionless movement. Collectively, the fibrocartilages, bursa, fat pad and the enthesis itself constitute the enthesis organ. However, it also includes both the immediately adjacent trabecular bone networks and in some cases deep fascia. The concept of a synovio-entheseal complex (SEC) and of a 'functional enthesis' are complimentary to that of an enthesis organ and also have important implications for understanding spondyloarthropathy. The SEC concept emphasizes the interdependence between synovial membrane and entheses within enthesis organs. It draws attention to the fact that one component (the enthesis) is prone to microdamage and the other (the synovium) to inflammation. If an enthesis is damaged, any ensuing inflammatory reaction is likely to occur in the synovium. The concept of a 'functional enthesis' serves to emphasise anatomical, biomechanical and pathological features that are shared between true fibrocartilaginous entheses and regions proximal to the attachment sites themselves where tendons or ligaments wrap around bony pulleys. Such'wrap-around regions' are well documented sites of pathology in SpA-for tenosynovitis is a recognized feature. Stress concentration at the enthesis itself is dissipated at many sites by fibrous connections between one tendon or ligament and another, close to the insertion site. At a microscopic level, enthesis fibrocartilage is of paramount importance in ensuring that fibre bending of the tendon or ligament is not focused at the hard tissue interface. Normal enthesis organs are avascular in their fibrocartilaginous regions, but tissue microdamage to entheses is common and appears to be associated with tissue repair responses and vessel ingrowth. This makes the enthesis organ a site where adjuvant molecules derived from bacteria may be preferentially deposited. This microdamage and propensity for bacterial molecule deposition in the context of genetic factors such as HLA-B27 appears to lead to the characteristic inflammatory changes of AS. Understanding the enthesis organ concept helps to explain synovitis and osteitis in spondyloarthropathy. An appreciation of the complex anatomy of 'articular enthesis organs' (e.g., that associated with the distal interphalangeal joints) is helpful in understanding disease patterns in psoriatic arthritis. In this chapter, we review the extent and types ofenthesis organs and show how a patho-anatomic appreciation of these structures leads to a new platform for understanding the pathogenesis of SpA.

Development of the human Achilles tendon enthesis organ

The attachment of the Achilles tendon is part of an 'enthesis organ' that reduces stress concentration at the hard-soft tissue interface. The organ also includes opposing sesamoid and periosteal fibrocartilages, a bursa and Kager's fat pad. In addition, the deep crural and plantar fasciae contribute to Achilles stress dissipation and could also be regarded as components. Here we describe the sequence in which these various tissues differentiate. Serial sections of feet from spontaneously aborted foetuses (crown rump lengths 22-322 mm) were examined. All slides formed part of an existing collection of histologically sectioned embryological material, obtained under Spanish law and housed in the Universidad Complutense, Madrid. From the earliest stages, it was evident that the Achilles tendon and plantar fascia had a mutual attachment to the calcaneal perichondrium. The first components of the enthesis organ to appear (in the 45-mm foetus) were the retrocalcaneal bursa and the crural fascia. The former developed by cavitation within the mesenchyme that later gave rise to Kager's fat pad. The tip of the putative fat pad protruded into the developing bursa in the 110-mm foetus and fully differentiated adipocytes were apparent in the 17-mm foetus. All three fibrocartilages were first recognisable in the 332-mm foetus--at which time adipogenesis had commenced in the heel fat pad. The sequence in which the various elements became apparent suggests that bursal formation and the appearance of the crural fascia may be necessary to facilitate the foot movements that subsequently lead to fibrocartilage differentiation. The later commencement of adipogenesis in the heel than in Kager's pad probably reflects the non-weight environment in utero. The direct continuity between plantar fascia and Achilles tendon that is characteristic of the adult reflects the initial attachment of both structures to the calcaneal perichondrium rather than to the skeletal anlagen itself.

Injection of dexamethasone versus placebo for lateral elbow pain: a prospective, double-blind, randomized clinical trial

PURPOSE

We tested the hypothesis that there is no difference in disability, pain, and grip strength 1 and 6 months after corticosteroid and lidocaine injection compared with lidocaine injection alone (placebo).

METHODS

Sixty-four patients were randomly assigned to dexamethasone (n = 31) or placebo (n = 33) injection. At enrollment, disability (Disabilities of the Arm, Shoulder, and Hand [DASH] questionnaire), pain on a visual analog scale, grip strength, depression (the Center for Epidemiologic Studies Depression Scale; CESD), and ineffective coping skills (the Pain Catastrophizing Scale; PCS) were comparable between treatment groups. At 1 and 6 months, DASH, pain, and grip strength measures were repeated. Univariate and multivariate analyses were used to determine predictors of disability. Analysis was by intention to treat.

RESULTS

One month after injection, DASH scores averaged 24 versus 27 points (dexamethasone vs placebo), pain 3.7 versus 4.3 cm, and grip strength 83% versus 87%. At 6 months, DASH scores averaged 18 versus 13 points, pain 2.4 versus 1.7 cm, and grip strength 98% versus 97%. CESD and PCS scores correlated with disability as measured by the DASH questionnaire. The best multivariate models included CESD at 1 month and PCS scores at 6 months and explained the majority of variability in DASH scores.

CONCLUSIONS

Corticosteroid injection did not affect the apparently self-limited course of lateral elbow pain. In secondary analyses in a subset of patients, perceived disability associated with lateral elbow pain correlated with depression and ineffective coping skills.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic I.

The transition from stiff to compliant materials in squid beaks

The beak of the Humboldt squid Dosidicus gigas represents one of the hardest and stiffest wholly organic materials known. As it is deeply embedded within the soft buccal envelope, the manner in which impact forces are transmitted between beak and envelope is a matter of considerable scientific interest. Here, we show that the hydrated beak exhibits a large stiffness gradient, spanning two orders of magnitude from the tip to the base. This gradient is correlated with a chemical gradient involving mixtures of chitin, water, and His-rich proteins that contain 3,4-dihydroxyphenyl-L-alanine (dopa) and undergo extensive stabilization by histidyl-dopa cross-link formation. These findings may serve as a foundation for identifying design principles for attaching mechanically mismatched materials in engineering and biological applications.

Magnetic resonance imaging of entheses. Part 1

Entheses are the sites of attachment of a tendon, ligament, or joint capsule to bone. Many features of entheses are adapted to disperse stress and accommodate compressive and shear forces at, or near, boundaries between tendons or ligaments and bone. Of particular interest is calcified and uncalcified fibrocartilage, which has mechanical properties that differ from those of tensile regions of tendons or ligaments, and from bone. Ultrashort echo time (UTE) pulse sequences can identify the specific tissue components of entheses and differentiate cortical bone, calcified fibrocartilage, uncalcified fibrocartilage, and fibrous connective tissue. Magic angle imaging can also differentiate tissues, such as fibrocartilage and tendon, which have different fibre orientations. Understanding the magnetic resonance (MR) appearance of entheses involves consideration of tissue properties, fibre-to-field angle, magic angle effects, pulse sequences, and geometrical factors including fibre-to-section orientation and partial volume effects. New approaches using MR imaging, allow entheses to be visualised with much greater detail than previously possible, and this may help in biomechanical studies, diagnosis of disease including overuse syndromes and spondyloarthropathies, as well as monitoring tissue repair and healing.

Structure-function relationships in tendons: a review

The purpose of the current review is to highlight the structure-function relationship of tendons and related structures to provide an overview for readers whose interest in tendons needs to be underpinned by anatomy. Because of the availability of several recent reviews on tendon development and entheses, the focus of the current work is primarily directed towards what can best be described as the 'tendon proper' or the 'mid-substance' of tendons. The review covers all levels of tendon structure from the molecular to the gross and deals both with the extracellular matrix and with tendon cells. The latter are often called 'tenocytes' and are increasingly recognized as a defined cell population that is functionally and phenotypically distinct from other fibroblast-like cells. This is illustrated by their response to different types of mechanical stress. However, it is not only tendon cells, but tendons as a whole that exhibit distinct structure-function relationships geared to the changing mechanical stresses to which they are subject. This aspect of tendon biology is considered in some detail. Attention is briefly directed to the blood and nerve supply of tendons, for this is an important issue that relates to the intrinsic healing capacity of tendons. Structures closely related to tendons (joint capsules, tendon sheaths, pulleys, retinacula, fat pads and bursae) are also covered and the concept of a 'supertendon' is introduced to describe a collection of tendons in which the function of the whole complex exceeds that of its individual members. Finally, attention is drawn to the important relationship between tendons and fascia, highlighted by Wood Jones in his concept of an 'ectoskeleton' over half a century ago - work that is often forgotten today.

Enhancement of the adolescent murine musculoskeletal system using low-level mechanical vibrations

Mechanical signals are recognized as anabolic to both bone and muscle, but the specific parameters that are critical to this stimulus remain unknown. Here we examined the potential of extremely low-magnitude, high-frequency mechanical stimuli to enhance the quality of the adolescent musculoskeletal system. Eight-week-old female BALB/cByJ mice were divided into three groups: baseline controls (BC, n = 8), age-matched controls (AC, n = 12), and whole body vibration (WBV, n = 12) at 45 Hz (0.3 g) for 15 min/day. Following 6 wk of WBV, bone mineralizing surfaces of trabeculae in the proximal metaphysis of the tibia were 75% greater (P < 0.05) than AC, while osteoclast activity was not significantly different. The tibial metaphysis of WBV mice had 14% greater trabecular bone volume (P < 0.05) than AC, while periosteal bone area, bone marrow area, cortical bone area, and the moments of inertia of this region were all significantly greater (up to 29%, P < 0.05). The soleus muscle also realized gains by WBV, with total cross-sectional area as well as type I and type II fiber area as much as 29% greater (P < 0.05) in mice that received the vibratory mechanical stimulus. The small magnitude and brief application of the noninvasive intervention emphasize that the mechanosensitive elements of the musculoskeletal system are not necessarily dependent on strenuous, long-term activity to initiate a structurally relevant response in the adolescent musculoskeletal system. If maintained into adulthood, the beneficial structural changes in trabecular bone, cortical bone, and muscle may serve to decrease the incidence of osteoporotic fractures and sarcopenia later in life.

Growth plate formation and development in alligator and mouse metapodials: evolutionary and functional implications

Mammalian metapodials (metacarpals and metatarsals), unlike most long bones, form a single growth plate, and undergo longitudinal growth at only one end. The growth dynamics of non-mammalian tetrapod metapodials have not been systematically examined in order to determine if unidirectional growth is unique to mammals. Here we compare murine metapodial ossification in growth stages that parallel those of embryonic, juvenile and subadult American alligators (Alligator mississippiensis). Safranin O staining was used for qualitative histology, and chondrocyte differentiation and proliferation were assessed via immunohistochemistry for type X collagen and proliferative cell nuclear antigen (PCNA). We establish that growth plates form at both ends of alligator metapodials and are maintained in the subadult. PCNA results show that alligators and mice share common patterns of chondrocyte proliferation during growth plate formation. In addition, while alligators and mice differ initially in the degree of organization and pace of chondrocyte differentiation, these parameters are largely similar in established growth plates. However, the replacement of cartilage by bone is highly irregular throughout growth in the alligator, in contrast to the more uniform process in the mouse. These results indicate that while alligators and mammals share common mechanisms of chondrocyte regulation, they differ substantially in their processes of ossification. Phylogenetic analysis indicates that the direct ossification of one epiphysis and reliance on a single growth plate is a derived character (synapomorphy) in therian mammals and likely indicates an adaptation for erect quadrupedal gait.

Different crimp patterns in collagen fibrils relate to the subfibrillar arrangement

Collagen fibril ultrastructure and course were examined in different connective tissues by PLM, SEM, TEM, and AFM. In tendons, collagen fibrils were large and heterogeneous with a straight subfibrillar arrangement. They ran densely packed, parallel, and straight changing their direction only in periodic crimps where fibrils showed a local deformation (fibrillar crimps). Other tissues such as aponeurosis, fascia communis, skin, aortic wall, and tendon and nerve sheaths showed thinner uniform fibrils with a helical subfibrillar arrangement. These fibrils appeared in parallel or helical arrangement following a wavy, undulating course. Ligaments showed large fibrils as in tendon, with fibrillar crimps but less packed. Thinner uniform-sized fibrils also were observed. Fibrillar crimps seem to be related to the subfibrillar arrangement being present only in large fibrils with a straight subfibrillar arrangement. These stiffer fibrils respond mainly to unidirectional tensional forces, whereas the flexible thinner fibrils with helical subfibrils can accommodate extreme curvatures without harm, thus responding to multidirectional loadings.

Poorer elbow proprioception in patients with lateral epicondylitis than in healthy controls: a cross-sectional study

Two groups of women, 15 patients with lateral epicondylitis and 21 healthy controls, were studied to compare proprioception in the elbows and knees between the groups. Outcome measures were absolute error and variable error for joint position sense and for threshold to detection of a passive movement. Both absolute error and variable error of threshold to detection of a passive movement were greater in the lateral epicondylitis-diagnosed elbows than in the controls' elbows (lateral epicondylitis, 1.8 degrees vs controls 1.1 degrees, P = .026; lateral epicondylitis, 0.8 degrees vs controls 0.3 degrees, P = .015), and there was a tendency toward a greater absolute error of joint position sense compared with the control elbows (lateral epicondylitis, 8.2 degrees vs controls, 5.6 degrees; P = .078). Absolute error of joint position sense was greater in the elbows than in the knees of the lateral epicondylitis patients, but no group differences were found for knees. Proprioception seems, therefore, to be poorer in elbows with lateral epicondylitis elbows than in the controls' elbows. This needs to be taken into consideration in the management of lateral epicondylitis.

Varied Presentations of Enthesopathy

BACKGROUND

The concept of "enthesis organ" allows a new look at the nature of enthesis involvement in some rheumatic and nonrheumatic systemic disorders.

OBJECTIVES

To describe the various presentations of enthesopathy in the course of systemic medical disorders using the available literature data.

METHODS

Review of relevant articles from 1996 to 2006 retrieved by a Medline search utilizing the index terms "enthesis," "enthesitis," and "tendonitis." The list of articles reviewed herein is not exhaustive, with preference given, where possible, to studies and surveys over case reports as well as the most recent literature reflecting new developments on the subject.

RESULTS

Enthesis is defined as the site of insertion of a tendon, ligament, fascia, or articular capsule into bone. Pain originating in the free nerve endings enriched entheses (enthesalgia) may represent a potential cause of chronic musculoskeletal pain in some individuals. Enthesis involvement in the disease process is well appreciated in spondyloarthropathies and in rheumatoid arthritis, though overshadowed by synovitis in the latter. Calcium deposition diseases may constitute the most significant articular cause of enthesopathies in the general population. New data may shed light on the possible pathophysiologic role of enthesopathy in the development of osteoarthritis. Various metabolic and endocrine conditions may manifest with enthesopathy features. The pathogenic mechanisms of enthesis involvement are not uniform and differ in the diverse disorders.

CONCLUSIONS

The concept of enthesopathy as a variety of syndromes in the course of many rheumatic, metabolic, and endocrine disorders should be appreciated. Exercise of a high level of suspicion toward enthesopathic involvement, and greater knowledge of enthesopathy's characteristic patterns and diagnostic possibilities, may allow better management of many patients in rheumatology practice.

The tooth attachment mechanism defined by structure, chemical composition and mechanical properties of collagen fibers in the periodontium

In this study, a comparison between structure, chemical composition and mechanical properties of collagen fibers at three regions within a human periodontium, has enabled us to define a novel tooth attachment mechanism. The three regions include, (1) the enthesis region: insertion site of periodontal ligament (PDL) fibers (collagen fibers) into cementum at the root surface, (2) bulk cementum, and (3) the cementum-dentin junction (CDJ). Structurally, continuity in collagen fibers was observed from the enthesis, through bulk cementum and CDJ. At the CDJ the collagen fibers split into individual collagen fibrils and intermingled with the extracellular matrix of mantle dentin. Under wet conditions, the collagen fibers at the three regions exhibited significant swelling suggesting a composition rich in polyanionic molecules such as glycosaminoglycans. Additionally, site-specific indentation illustrated a comparable elastic modulus between collagen fibers at the enthesis (1-3 GPa) and the CDJ (2-4 GPa). However, the elastic modulus of collagen fibers within bulk cementum was higher (4-7 GPa) suggesting presence of extrafibrillar mineral. It is known that the tooth forms a fibrous joint with the alveolar bone, which is termed a gomphosis. Although narrower in width than the PDL space, the hygroscopic CDJ can also be termed as a gomphosis; a fibrous joint between cementum and root dentin capable of accommodating functional loads similar to that between cementum and alveolar bone. From an engineering perspective, it is proposed that a tooth contains two fibrous joints that accommodate the masticatory cyclic loads. These joints are defined by the attachment of dissimilar materials via graded stiffness interfaces, such as: (1) alveolar bone attached to cementum with the PDL; and (2) cementum to root dentin with the CDJ. Thus, through variations in concentrations of basic constituents, distinct regions with characteristic structures and graded properties allow for attachment and the load bearing characteristics of a tooth.

The structure of the coracoacromial ligament: fibrocartilage differentiation does not necessarily mean pathology

The coracoacromial ligament forms part of the coracoacromial arch and is implicated in impingement syndrome and acromial spur formation. Here, we describe its structure and the composition of its extracellular matrix. Ligaments were obtained from 15 cadavers, nine from older people (average age 74.7 years) and six from younger individuals (average age 24.2 years). Cryosections of methanol-fixed tissue were cut and sections were immunolabelled with monoclonal antibodies against collagens, glycosaminoglycans, proteoglycans, matrix proteins and neurofilament proteins. Both ligament entheses were highly fibrocartilaginous and immunolabelled strongly for type II collagen, aggrecan and link protein. The area of labelling was more extensive in older people. However, fibrocartilage also characterized the ligament midsubstance, particularly with increased age. Signs of fibrocartilage degeneration were more common in older people. Ligament fat (containing blood vessels and nerve fibers) was conspicuous in both age groups, especially between fiber bundles at the entheses. We conclude that fibrocartilage is a normal feature but becomes more pronounced with age. It is not necessarily pathological, for it simply indicates that the ligament is subject to compression and/or shear. Nevertheless, the prominence of fibrocartilage at the acromial enthesis may relate to the frequency with which enthesophytes develop.

Tenocyte responses to mechanical loading in vivo: a role for local insulin-like growth factor 1 signaling in early tendinosis in rats

OBJECTIVE

To investigate tenocyte regulatory events during the development of overuse supraspinatus tendinosis in rats.

METHODS

Supraspinatus tendinosis was induced by running rats downhill at 1 km/hour for 1 hour a day. Tendons were harvested at 4, 8, 12, and 16 weeks and processed for brightfield, polarized light, or transmission electron microscopy. The development of tendinosis was assessed semiquantitatively using a modified Bonar histopathologic scale. Apoptosis and proliferation were examined using antibodies against fragmented DNA or proliferating cell nuclear antigen, respectively. Insulin-like growth factor 1 (IGF-1) expression was determined by computer-assisted quantification of immunohistochemical reaction. Local IGF-1 signaling was probed using antibodies to phosphorylated insulin receptor substrate 1 (IRS-1) and ERK-1/2.

RESULTS

Tendinosis was present after 12 weeks of downhill running and was characterized by tenocyte rounding and proliferation as well as by glycosaminoglycan accumulation and collagen fragmentation. The proliferation index was elevated in CD90+ tenocytes in association with tendinosis and correlated with increased local IGF-1 expression by tenocytes and phosphorylation of IRS-1 and ERK-1/2. Both apoptosis and cellular inflammation were absent at all time points.

CONCLUSION

In this animal model, early tendinosis was associated with local stimulation of tenocytes rather than with extrinsic inflammation or apoptosis. Our data suggest a role for IGF-1 in the load-induced tenocyte responses during the pathogenesis of overuse tendon disorders.

Magnetic resonance imaging of entheses using ultrashort TE (UTE) pulse sequences

The attachment of tendons, ligaments, and joint capsule to bone (entheses) is reviewed and new options for visualizing key components of entheses provided by ultrashort TE (UTE) pulse sequences are described. Many features of entheses are adapted to the dispersion of stress at the boundary between tendons/ligaments and bone. Of particular interest is fibrocartilage, which has mechanical properties different from those of both "pure" tendon/ligament and bone. Features typical of entheses can also be seen at sites where tendons or ligaments are in contact with (but not attached to) bone, and the concept of a "functional enthesis" has been developed to emphasize the similarities. The enthesis concept has also been broadened to include the idea of an "enthesis organ" in which many tissues play a role in dissipating stress concentration. UTE pulse sequences can specifically identify the calcified and uncalcified fibrocartilage tissue components of entheses and differentiate these from fibrous connective tissue and bone. These tissues cannot be separately visualized at entheses with conventional pulse sequences. Entheses are involved in overuse syndromes and seronegative spondyloarthropathies (SpA) and there are important issues related to tissue repair and healing following surgery.

The magic angle effect: A source of artifact, determinant of image contrast, and technique for imaging

This review provides a formalism for understanding magic angle effects in clinical studies. It involves consideration of the fiber-to-field angle for linear structures such as tendons, ligaments, and peripheral nerves, disc-like and circular structures such as menisci and labra, as well as complex three-dimensional structures. There may be one or more fiber types with different orientations within each of these tissues. The orientation of these fibers to B(0) is crucial in determining their magic angle effect. Tissues may show a variety of appearances depending on their baseline T2, as well as the increase in T2 produced by the magic angle effect. The appearances are affected by TE, which affects both the general tissue signal level and the change in signal produced by the magic angle effect, fiber-to-slice orientation, and partial volume effects. Deliberate positioning of structures and tissues at particular orientations to B(0) can be used to increase the signal from tissues such as tendons and ligaments and so allow them to be imaged with conventional sequences. The technique can also be used to produce contrast between tissues with fibers that have different orientations to B(0).

Proteins in load-bearing junctions: the histidine-rich metal-binding protein of mussel byssus

Building complex load-bearing scaffolds depends on effective ways of joining functionally different biomacromolecules. The junction between collagen fibers and foamlike adhesive plaques in mussel byssus is robust despite the strikingly dissimilar connected structures. mcfp-4, the matrix protein from this junction, and its presecreted form from the foot tissue of Mytilus californianus were isolated and characterized. mcfp-4 has a mass of approximately 93 kDa as determined by MALDI-TOF mass spectrometry. Its composition is dominated by histidine (22 mol %), but levels of lysine, arginine, and aspartate are also significant. A small amount of 3,4-dihydroxyphenyl-l-alanine (2 mol %) can be detected by amino acid analysis and redox cycling assays. The cDNA-deduced sequence of mcfp-4 reveals multiple variants with highly repetitive internal structures, including approximately 36 tandemly repeated His-rich decapeptides (e.g., HVHTHRVLHK) in the N-terminal half and 16 somewhat more degenerate aspartate-rich undecapeptides (e.g., DDHVNDIAQTA) in the C-terminal half. Incubation of a synthetic peptide based on the His-rich decapeptide with Fe3+, Co2+, Ni2+, Zn2+, and Cu2+ indicates that only Cu is strongly bound. MALDI-TOF mass spectrometry of the peptide modified with diethyl pyrocarbonate before and after Cu binding suggests that histidine residues dominate Cu binding. In contrast, the aspartate-rich undecapeptides preferentially bind Ca2+. mcfp-4 is strategically positioned to function as a macromolecular bifunctional linker by using metal ions to couple its own His-rich domains to the His-rich termini of the preCOLs. Ca2+ may mediate coupling of the C-terminus to other calcium-binding plaque proteins.

Expression of extracellular matrix molecules typical of articular cartilage in the human scapholunate interosseous ligament

The scapholunate interosseous ligament (SLIL) connects the scaphoid and lunate bones and plays a crucial role in carpal kinematics. Its rupture leads to carpal instability and impairment of radiocarpal joint function. As the ligament is one of the first structures affected in rheumatoid arthritis, we conducted an immunohistochemical study of cadaveric tissue to determine whether it contains known autoantigens for rheumatoid arthritis. We immunolabelled the ligament from one hand in 12 cadavers with monoclonal antibodies directed against a wide range of extracellular matrix (ECM) molecules associated with both fibrous and cartilaginous tissues. The labelling profile has also enabled us to comment on how the molecular composition of the ligament relates to its mechanical function. All regions of the ligament labelled for types I, III and VI collagens, chondroitin 4 and 6 sulphates, keratan sulphate, dermatan sulphate, versican, tenascin and cartilage oligomeric matrix protein (COMP). However, both entheses labelled strongly for type II collagen, aggrecan and link protein and were distinctly fibrocartilaginous. In some regions, the ligament attached to bone via a region of hyaline cartilage that was continuous with articular cartilage. Labelling for cartilage molecules in the midsubstance was most evident dorsally. We conclude that the SLIL has an ECM which is typical of other highly fibrocartilaginous ligaments that experience both tensile load and shear. The presence of aggrecan, link protein, COMP and type II collagen could explain why the ligament may be a target for autoantigenic destruction in some forms of rheumatoid arthritis.

Microdamage and altered vascularity at the enthesis–bone interface provides an anatomic explanation for bone involvement in the HLA–B27–associated spondylarthritides and allied disorders

OBJECTIVE

To describe the basis for entheseal-associated bone disease in the spondylarthritides, by analyzing microanatomic and histopathologic relationships between soft tissue, bone cortex, and adjacent trabeculae.

METHODS

Serial sections from 52 entheses were examined; these entheses encompassed small and large insertions in the upper limb (n = 21), lower limb (n = 27), and spine (n = 4) from 60 cadavers. Enthesis microdamage (fissuring) as well as vascular and reparative changes were evaluated. Contact radiographs were used to ascertain the relationship between entheses and the trabecular network.

RESULTS

At virtually all fibrocartilaginous entheses, the deep cortical boundary was extremely thin (typically 50-600 microm) or indistinguishable, and 96% of entheses had small holes in the cortical shell (typically 100-400 microm wide). Such regions were frequent sites of bone formation and renewal (96%) and microdamage (31%); these changes were more common in the lower limb. The presence of blood vessels near holes in the cortical shell was common; in 85% of attachments, blood vessels were present on the soft tissue side of the enthesis. Highly orientated trabeculae were more obvious in the lower limb than the upper limb (59% versus 29%).

CONCLUSION

The trabecular network supporting the cortical shell is an integral part of the enthesis, transferring load to an extensive skeletal region. In many cases, tendons/ligaments are anchored directly to such networks. This functional integration is associated with microdamage and repair at the hard tissue-soft tissue interface. These findings have implications for understanding bone involvement in SpA and for the SpA concept in general, especially the hypothesis that enthesis-bone architecture may be important in disease initiation.