Mechanics of coracoacromial ligament transfer augmentation for acromioclavicular joint injuries

The objective of this study was to determine how effectively the Weaver-Dunn repair (both unaugmented and augmented with a suture and suture anchor) restores joint translation in response to applied loads to normal. Translation of a reference point on the clavicle relative to a reference point on the acromion was assessed in five cadaver shoulders by applying anterior, posterior and superior loads of 50 N to the clavicle using a specially designed test rig while measuring movement of the acromion and clavicle with an optical measurement system. Translation was determined for the intact joint, after simulated injury and Weaver-Dunn repair, and after augmentation of the Weaver-Dunn repair with a suture fixed to a suture anchor in the coracoid process. Joints were significantly more mobile after Weaver-Dunn repair (16.1 mm anterior, 15.7 mm posterior, 11.1 mm superior) than when intact (4.1 mm anterior, 3.2 mm posterior, 4.0 mm superior) (p < 0.005). Augmentation with a suture and suture anchor reduced separation of the Weaver-Dunn reconstruction significantly (to 5.3 mm anterior, 4.1 mm posterior, 2.0 mm superior) (p < 0.005). Joints reconstructed using an augmented Weaver-Dunn repair were not significantly more (or less) mobile than normal joints (p > 0.005), although the power of the test to detect this difference was low (power = 0.107). We anticipate that, when surgery is indicated for treating acromioclavicular joint injury, an augmented Weaver-Dunn reconstruction will yield a joint that is less painful, more functional and less likely to require revision.     

Simple method for reconstruction of the cleft hand with an adducted thumb.

We describe a new, simple method for reconstruction of a cleft hand. Ulnar transposition of the index ray followed by creation of a thumb web space is an effective way to get sufficient abduction of the thumb. This procedure is simpler than the traditional "translocation of the flap," and also it produces no circulatory troubles to worry about.     

Avulsion injuries of the thumb

Avulsion amputations of the thumb are generally thought to have a worse prognosis after replantation than other amputations. We report the results of 17 thumbs that had an avulsion amputation and were replanted. Fourteen of the 17 survived (82 percent). Our experience indicated that the survival rate was improved by restoring continuity of at least two veins and two arteries, using a Y-shaped vein graft and the princeps pollicis artery for the source of arterial circulation. Nerve grafts were used to bridge defects in avulsed digital nerves. When possible, avulsed tendons were reattached to their muscle. Key pinch strength was 60 percent of normal, and grip strength was always less than that of the normal hand. The age of the patients and the cold ischemia time had no significant effect on either survival or function of the replanted thumb. When excellent venous backflow occurred immediately after the vessel repair and continued for at least 20 minutes, the thumb always survived without complications.     

Proteoglycan metabolism during repair of the ruptured medial collateral ligament in skeletally mature rabbits

The metabolism of the chondroitin/dermatan sulfate (CS/DS) proteoglycans (PGs) decorin and biglycan is markedly altered during short-term (3-6 weeks) and long-term (40 weeks-2 years) repair of surgically ruptured medial collateral ligaments from mature rabbits. A PG-rich extracellular matrix accumulates in injury gaps by 3 weeks postsurgery and extends into tissue regions containing the original ligaments, and elevated PG levels remain apparent up to 2 years postinjury. CS/DS PGs were prepared from such ligaments and identified after SDS-polyacrylamide gel electrophoresis by Alcian blue staining or immunoblotting. In normal ligaments, decorin is the most abundant proteoglycan (accounting for approximately 80% of the total); the remainder is biglycan and a large PG, possibly versican. In repairing ligaments, decorin is barely detected, but instead a large proteoglycan and abundant amounts of biglycan accumulate. Biglycan is present in two forms in repairing ligaments, and they can be separated on SDS-PAGE into 200- and 140-kDa forms. The slower migrating species is absent in normal ligaments and may represent a different glycoform (containing either a single or two short chondroitin/dermatan sulfate chains) of biglycan. Alteration in PG expression and posttranslational processing during medial collateral ligament repair are similar to those reported for repair and scar formation of other connective tissues. The accumulation of biglycan observed here may interfere with proper collagen network remodeling and may lead to persistent inflammatory and matrix turnover processes, thus preventing restoration of a long-term functional ligament tissue.     

A mathematical model of medial collateral ligament repair: migration,fibroblast proliferation and collagen formation

The partial rupture of ligament fibres leads to an injury known as grade 2 sprain. Wound healing after injury consists of four general stages: swelling, release of platelet-derived growth factor (PDGF), fibroblast migration and proliferation and collagen production. The aim of this paper is to present a mathematical model based on reaction–diffusion equations for describing the repair of the medial collateral ligament when it has suffered a grade 2 sprain. We have used the finite element method to solve the equations of this. The results have simulated the tissue swelling at the time of injury, predicted PDGF influence, the concentration of fibroblasts migrating towards the place of injury and reproduced the random orientation of immature collagen fibres. These results agree with experimental data reported by other authors. The model describes wound healing during the 9 days following such injury.     

A mathematical model of medial collateral ligament repair: migration, fibroblast proliferation and collagen formation

The partial rupture of ligament fibres leads to an injury known as grade 2 sprain. Wound healing after injury consists of four general stages: swelling, release of platelet-derived growth factor (PDGF), fibroblast migration and proliferation and collagen production. The aim of this paper is to present a mathematical model based on reaction-diffusion equations for describing the repair of the medial collateral ligament when it has suffered a grade 2 sprain. We have used the finite element method to solve the equations of this. The results have simulated the tissue swelling at the time of injury, predicted PDGF influence, the concentration of fibroblasts migrating towards the place of injury and reproduced the random orientation of immature collagen fibres. These results agree with experimental data reported by other authors. The model describes wound healing during the 9 days following such injury.     

Temperature dependent behavior of the canine medial collateral ligament

The temperature dependent tensile behavior of ligament was investigated from 2 degrees C to 37 degrees C. Nondestructive cyclic tests were performed on ten canine femur-medial collateral ligament-tibia (FMT) complexes at sequential temperatures of 22 degrees C, 22 degrees C, 27 degrees C, 32 degrees C, 37 degrees C, and again at 22 degrees C. The samples were rested at zero load between tests for sufficient time periods to allow for full recovery from the ligament's time and history dependent viscoelastic properties. Ten additional FMT complexes were sequentially tested in a similar fashion, but at temperatures of 22 degrees C, 22 degrees C, 2 degrees C, 6 degrees C, 14 degrees C, and 22 degrees C. All canine FMT complexes showed temperature dependent viscoelastic properties: the measured area of hysteresis decreased with increasing temperature; the cyclic load relaxation behavior plateaued to a higher value at lower temperatures; and the tensile load at a predetermined ligament substance strain level had an inversely proportional relationship with respect to temperature.     

Material characterization of human medial collateral ligament.

The objectives of this study were to determine the longitudinal and transverse material properties of the human medial collateral ligament (MCL) and to evaluate the ability of three existing constitutive models to describe the material behavior of MCL. Uniaxial test specimens were punched from ten human cadaveric MCLs and tensile tested along and transverse to the collagen fiber direction. Using load and optical strain analysis information, the tangent modulus, tensile strength and ultimate strain were determined. The material coefficients for each constitutive model were determined using nonlinear regression. All specimens failed within the substance of the tissue. Specimens tested along the collagen fiber direction exhibited the typical nonlinear behavior reported for ligaments. This behavior was absent from the stress-strain curves of the transverse specimens. The average tensile strength, ultimate strain, and tangent modulus for the longitudinal specimens was 38.6 +/- 4.8 MPa, 17.1 +/- 1.5 percent, and 332.2 +/- 58.3 MPa, respectively. The average tensile strength, ultimate strain, and tangent modulus for the transverse specimens was 1.7 +/- 0.5 MPa, 11.7 +/- 0.9 percent, and 11.0 +/- 3.6 MPa, respectively. All three constitutive models described the longitudinal behavior of the ligament equally well. However, the ability of the models to describe the transverse behavior of the ligament varied.     

Biomechanical validation of finite element models for two silicone metacarpophalangeal joint implants

Silicone implants are used for prosthetic arthroplasty of metacarpophalangeal (MCP) joints severely damaged by rheumatoid arthritis. Different silicone elastomer MCP implant designs have been developed, including the Swanson and the NeuFlex implants. The goal of this study was to compare the in vitro mechanical behavior of Swanson and NeuFlex MCP joint implants. Three-dimensional (3D) finite element (FE) models of the silicone implants were modeled using the commercial software ANSYS and subjected to angular displacement from 0 deg to 90 deg. FE models were validated using mechanical tests of implants incrementally bent from 0 deg to 90 deg in a joint simulator. Swanson size 2 and 4 implants were compared with NeuFlex size 10 and 30 implants, respectively. Good agreement was observed throughout the range of motion for the flexion bending moment derived from 3D FE models and mechanical tests. From 30 deg to 90 deg, the Swanson 2 demonstrated a greater resistance to deformation than the NeuFlex 10 and required a greater bending moment for joint flexion. For larger implant sizes, the NeuFlex 30 had a steeper moment-displacement curve, but required a lower moment than the Swanson 4, due to implant preflexion. On average, the stress generated at the implant hinge from 30 deg to 90 deg was lower in the NeuFlex than in the Swanson. On average, starting from the neutral position of 30 deg for the preflexed NeuFlex implant, higher moments were required to extend the NeuFlex implants to 0 deg compared with the Swanson implants, which returned spontaneously to resting position. Implant toggling within the medullary canals was less in the NeuFlex than in the Swanson. The differential performance of these implants may be useful in implant selection based on the preoperative condition(s) of the joint and specific patient functional needs.     

Intrinsic and extrinsic contributions to the passive moment at the metacarpophalangeal joint

The purpose of this investigation was to determine whether the passive range of motion at the finger joints is restricted more by intrinsic tissues (cross a single joint) or by extrinsic tissues (cross multiple joints). The passive moment at the metacarpophalangeal (MP) joint of the index finger was modeled as the sum of intrinsic and extrinsic components. The intrinsic component was modeled only as a function of MP joint angle. The extrinsic component was modeled as a function of MP joint angle and wrist angle. With the wrist fixed in seven different positions the passive moment at the MP joint of eight subjects was recorded as the finger was rotated through its range at a constant rate. The moment-angle data were fit by the model and the extrinsic and intrinsic components were calculated for a range of MP joint angles and wrist positions. With the MP joint near its extension limit, the median percent extrinsic contribution was 94% with the wrist extended 60° and 14% with the wrist flexed 60°. These percentages were 40 and 88%, respectively, with the MP joint near its flexion limit. Our findings indicate that at most wrist angles the extrinsic tissues offer greater restraint at the limits of MP joint extension and flexion than the intrinsic tissues. The intrinsic tissues predominate when the wrist is flexed or extended enough to slacken the extrinsic tissues. Additional characteristics of intrinsic and extrinsic tissues can be deduced by examining the parameter values calculated by the model.     

Structural properties of the medial collateral ligament complex of the human knee

The anatomy of the medial collateral ligament (MCL) complex consists of three identifiable passive restraining structures: the longitudinal fibres of the superficial medial collateral ligament (sMCL), the deep medial collateral ligament (dMCL), and the posteromedial capsule (PMC). The purpose of this study was to measure and compare the structural properties of these three individual structures. Eight human cadaveric knees (age 72-89 years, mean = 77 years, S.D. 5.3) were harvested and bone-ligament-bone tensile testing specimens prepared. After preconditioning, the specimens were extended to failure at 1000 mm/min in an Instron tensile testing machine. Ligament bundles failed either mid-substance or at their bony attachments. The ligament bundles had maximum loads of 534 N (sMCL), 194 N (dMCL), 425 N (PMC) and failed at 10.2, 7.1, and 12.0 mm mean extension, respectively. The maximum load and linear stiffness of the sMCL were significantly higher than those of the dMCL but not the PMC. The maximum load of the PMC was significantly higher than that of the dMCL; the linear stiffness of the PMC was higher than that of the dMCL but this did not reach statistical significance. The dMCL failed at a significantly lower extension than the other structures. The sMCL bundles that failed at their bony attachment were remounted using a freezing clamp fixture and again extended to failure, resulting in mid-substance failure at 884 N (74% higher). This study has shown that the PMC of the knee has comparable structural properties to the long superficial MCL and the short, deep MCL. In summary, the structural properties of the different component structures of the medial ligament complex indicate possible functional significance.