Donald K. Bynum

IL-1β induces COX2, MMP-1, -3 and -13, ADAMTS-4, IL-1β and IL-6 in human tendon cells

Overuse injuries and trauma in tendon often involve acute or chronic pain and eventual matrix destruction. Anti‐inflammatory drugs have been used as a treatment, however, the cellular and molecular mechanisms of the destructive processes in tendon are not clearly understood. It is thought that an inflammatory event may be involved as an initiating factor. Mediators of the inflammatory response include cytokines released from macrophages and monocytes. Interleukin‐1 beta (IL‐1β) is a candidate proinflammatory cytokine that is active in connective tissues such as bone and cartilage. We hypothesized that tendon cells would express receptors and respond to IL‐1β in an initial „molecular inflammation”︁ cascade, that is, connective tissue cell expression of cytokines that induce matrix destructive enzymes. This cascade results in expression of matrix metalloproteinases (MMPs) and aggrecanases that may lead to matrix destruction. Normal human tendon cells from six patients were isolated, grown to quiescence and treated with human recombinant IL‐1β in serum‐free medium for 16 h. Total RNA was isolated and mRNA expression assessed by semi‐quantitative RT‐PCR. IL‐1β (1 nM) induced mRNAs for cyclooxygenase 2 (COX2), MMP‐1, ‐3, ‐13 and aggrecanase‐1 as well as IL‐1β and IL‐6, whereas mRNAs for COX1 and MMP‐2 were expressed constitutively. The IL‐1β‐treated tendon cells released prostaglandin E2 (PGE2) in the medium, suggesting that the inducible COX2 catalyzed this synthesis. Induction of PGE2 was detectable at 10 pM IL‐1β. IL‐1β also stimulated MMP‐1 and ‐3 protein secretion. Induction of MMP‐1 and ‐3 was detectable at 10 pM IL‐1β. Post‐injury or after some other inciting events, exogenous IL‐1β released upon bleeding or as leakage of local capillaries may drive a proinflammatory response at the connective tissue cell level. The resulting induction of COX2, MMP‐1 and ‐3 may underscore a potential for nonlymphocyte‐mediated cytokine production of MMPs that causes matrix destruction and a loss of tendon biomechanical properties. Endogenous IL‐1β might contribute to the process through a positive feedback loop by stimulating expression and accumulation of MMPs in the tendon matrix.

ATP modulates load-inducible IL-1β, COX 2, and MMP-3 gene expression in human tendon cells

Tendon cells receive mechanical signals from the load bearing matrices. The response to mechanical stimulation is crucial for tendon function. However, overloading tendon cells may deteriorate extracellular matrix integrity by activating intrinsic factors such as matrix metalloproteinases (MMPs) that trigger matrix destruction. We hypothesized that mechanical loading might induce interleukin‐1beta (IL‐1β) in tendon cells, which can induce MMPs, and that extracellular ATP might inhibit the load‐inducible gene expression. Human tendon cells isolated from flexor digitorum profundus tendons (FDPs) of four patients were made quiescent and treated with ATP (10 or 100 μM) for 5 min, then stretched equibiaxially (1 Hz, 3.5% elongation) for 2 h followed by an 18‐h‐rest period. Stretching induced IL‐1β, cyclooxygenase 2 (COX 2), and MMP‐3 genes but not MMP‐1. ATP reduced the load‐inducible gene expression but had no effect alone. A medium change caused tendon cells to secrete ATP into the medium, as did exogenous UTP. The data demonstrate that mechanical loading induces ATP release in tendon cells and stimulates expression of IL‐1β, COX 2, and MMP‐3. Load‐induced endogenous IL‐1β may trigger matrix remodeling or a more destructive pathway(s) involving IL‐1β, COX 2, and MMP‐3. Concomitant autocrine and paracrine release of ATP may serve as a negative feedback mechanism to limit activation of such an injurious pathway. Attenuation or failure of this negative feedback mechanism may result in the progression to tendinosis.

Gap junctions regulate responses of tendon cells ex vivo to mechanical loading.

Avian digital flexor tendons were used with a device to apply load ex vivo to study the effects on deoxyribonucleic acid and collagen synthesis when cell to cell communication is blocked. Flexor digitorum profundus tendons from the middle toe of 52-day-old White Leghorn chickens were excised and used as nonloaded controls, or clamped in the jaws of a displacement controlled tissue loading device and mechanically loaded for 3 days at a nominal 0.65% elongation at 1 Hz for 8 hours per day with 16 hours rest. Tendon samples were radiolabeled during the last 16 hours with 3H-thymidine to monitor deoxyribonucleic acid synthesis or with 3H-proline to radiolabel newly synthesized collagen. Cyclic loading of whole avian flexor tendons stimulated deoxyribonucleic acid and collagen synthesis, which could be blocked with octanol, a reversible gap junction blocker. Cells from human digital flexor tendon were used to populate a rectangular, three-dimensional, porous, polyester foam that could be deformed cyclically in vitro. Together, these results support the hypothesis that tendon cells must communicate to sustain growth and matrix expression and that an engineered three-dimensional construct can be used to study responses to mechanical load in vitro.

Closed traumatic rupture of finger flexor pulleys

Nine patients are described with closed traumatic rupture of the digital flexor pulley system. All presented with significant flexion contractures of the proximal interphalangeal joint and bow-stringing of the flexor tendons. In seven patients, the pathology was verified at surgery and pulley reconstruction provided a good result. The diagnoses in the other patients, treated conservatively, were verified by tenogram and magnetic resonance imaging.

Malunion of the distal radius.

Fractures of the distal radius are common injuries. Acceptable results typically can be obtained with appropriate surgical or nonsurgical management. However, a small percentage of these fractures can progress to symptomatic malunion, which traditionally has been treated with osteotomy of the distal radius. Proper understanding of anatomy, biomechanics, indications, and contraindications can help guide patient selection for surgery. In formulating a treatment plan, the surgeon also must consider such technical variables as the type of osteotomy, the use of bone graft or bone-graft substitute, and the means of fixation to stabilize the osteotomy. Simultaneous implementation of an ulnar-side procedure, an intra-articular osteotomy, and soft-tissue releases also may be necessary. Some cases may be more appropriate for wrist fusion or other salvage procedures.

Management of Intra-Articular Metacarpal Base Fractures of the Second Through Fifth Metacarpals

Intra-articular fractures of the second through fifth metacarpal bases are uncommon injuries but can result in serious morbidity if improperly managed. These injuries usually occur because of forced flexion of the wrist with simultaneous extension of the arm, as occurs with a punch or a fall. As there are few large series of reports for these injuries, there is no consensus in the current literature on the most appropriate treatment for them. Whereas some authors have reported successful results after closed reduction, many recommend open reduction with internal fixation to ensure the integrity of the tendinous insertions of the extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris. This article reviews the case reports and case series extant in the literature concerning intra-articular fractures of the bases of the second through fifth metacarpals, and it provides important diagnostic and management considerations for these injuries.

Flexor tendon sheath infections of the hand

Abstract Flexor tendon sheath infections of the hand must be diagnosed and treated expeditiously to avoid poor clinical outcomes. Knowledge of the sheaths anatomy is essential for diagnosis and to help to guide treatment. The Kanavel cardinal signs are useful for differentiating conditions with similar presentations. Management of all but the earliest cases of pyogenic flexor tenosynovitis consists of intravenous antibiotics and surgical drainage of the sheath with open or closed irrigation. Closed irrigation may be continued postoperatively. Experimental data from an animal study have shown that local administration of antibiotics and/or corticosteroids can help lessen morbidity from the infection; however, additional research is required. Despite aggressive and prompt antibiotic therapy and surgical intervention, even otherwise healthy patients can expect some residual digital stiffness following flexor tendon sheath infection. Patients with medical comorbidities or those who present late with advanced infection can expect poorer outcomes, including severe digital stiffness or amputation.

Long-term outcome of Volz total wrist arthroplasties

The authors determined the outcomes of 18 consecutive Volz total wrist arthroplasties that were followed for an average of 8.6 years. Nine of these wrists were followed for 10 or more years. Fourteen wrists were replaced for rheumatoid arthritis and four for post-traumatic degenerative joint disease. Forty-nine degrees of combined flexion and extension and 25 degrees of combined ulnar and radial deviation were maintained. The balance of wrist motion was dependent upon the design and location of the metacarpal prosthesis. A 24% loss in carpal height (subsidence) occurred during the study period. Four metacarpal components were loose (22%), three of which were placed in patients with degenerative joint disease. One radial component (6%) was loose. Fifteen of 18 wrists (83%) had little or no pain. The three wrists with moderate or severe pain were in patients with degenerative joint disease. There were five (28%) complications. One revision was performed and another was recommended. Overall, the long-term outcome of total wrist arthroplasty was favorable in patients with rheumatoid arthritis.

Repair of peripheral nerves with the argon laser. A functional and histological evaluation.

A technique for repair of peripheral nerves with the argon laser was evaluated with regard to functional and histological recovery. The results were compared with those of reconstruction by a microsurgical epineurial-suture technique. The terminal branch of the peroneal nerve to the extensor digitorum longus in thirty-three New Zealand White rabbits served as the experimental model. Histology and neuromuscular function were evaluated at one, two, and six months after repair. When the diameters of the axons and the morphology distal to the site of repair were evaluated, the nerves that had been repaired with the laser more closely resembled those of the control rabbits. Examination of the site of repair also revealed less foreign-body reaction and axonal outgrowth in the laser-repaired nerves than in those that had been reconstructed with epineurial suture. Neuromuscular function was evaluated by measurement of the force of contraction of the extensor digitorum longus after electrical stimulation of the nerve proximal to the site of repair. Functional recovery paralleled the histological findings. At one month, there was no difference in the neuromuscular function that had been achieved with either technique. At two months, the laser-repaired nerves began to show increased muscular strength at higher frequencies of stimulation (sixteen and thirty-two hertz). Six months postoperatively, the nerves that had been repaired with the laser had consistently better neuromuscular function than those that had been repaired by epineurial suture. The improvement was most marked at higher voltages of stimulation (threshold multiplied by ten) and at frequencies of stimulation of more than sixteen hertz.

Mechanical loading stimulates ecto-ATPase activity in human tendon cells

Response to external stimuli such as mechanical signals is critical for normal function of cells, especially when subjected to repetitive motion. Tenocytes receive mechanical stimuli from the load‐bearing matrix as tension, compression, and shear stress during tendon gliding. Overloading a tendon by high strain, shear, or repetitive motion can cause matrix damage. Injury may induce cytokine expression, matrix metalloproteinase (MMP) expression and activation resulting in loss of biomechanical properties. These changes may result in tendinosis or tendinopathy. Alternatively, an immediate effector molecule may exist that acts in a signal‐dampening pathway. Adenosine 5′‐triphosphate (ATP) is a candidate signal blocker of mechanical stimuli. ATP suppresses load‐inducible inflammatory genes in human tendon cells in vitro. ATP and other extracellular nucleotide signaling are regulated efficiently by two distinct mechanisms: purinoceptors via specific receptor–ligand binding and ecto‐nucleotidases via the hydrolysis of specific nucleotide substrates. ATP is released from tendon cells by mechanical loading or by uridine 5′‐triphosphate (UTP) stimulation. We hypothesized that mechanical loading might stimulate ecto‐ATPase activity. Human tendon cells of surface epitenon (TSC) and internal compartment (TIF) were cyclically stretched (1 Hz, 0.035 strain, 2 h) with or without ATP. Aliquots of the supernatant fluids were collected at various time points, and ATP concentration (ATP) was determined by a luciferin‐luciferase bioluminescence assay. Total RNA was isolated from TSC and TIF (three patients) and mRNA expression for ecto‐nucleotidase was analyzed by RT‐PCR. Human tendon cells secreted ATP in vitro (0.5–1 nM). Exogenous ATP was hydrolyzed within minutes. Mechanical load stimulated ATPase activity. ATP was hydrolyzed in mechanically loaded cultures at a significantly greater rate compared to no load controls. Tenocytes (TSC and TIF) expressed ecto‐nucleotidase mRNA (ENTPD3 and ENPP1, ENPP2). These data suggest that motion may release ATP from tendon cells in vivo, where ecto‐ATPase may also be activated to hydrolyze ATP quickly. Ecto‐ATPase may act as a co‐modulator in ATP load‐signal modulation by regulating the half‐life of extracellular purine nucleotides. The extracellular ATP/ATPase system may be important for tendon homeostasis by protecting tendon cells from responding to excessive load signals and activating injurious pathways.