J. R. Parsons

The viscoelastic shear behavior of normal rabbit articular cartilage

Abstract A theoretical solution ‡ for the indentation of a layered medium by an axisymmetric plane-ended ram has been applied in the in vitro study of the mechanical properties of the articular surface of the distal femur of the rabbit. Experimental results directly yield shear moduli and retardation spectra which are invariant with respect to cartilage thickness and applied stress within the stress range used. The success of this theory, coupled with the simplicity and reproducibility of the test, suggests that this method has wide applicability in the study of experimentally or pathologically altered cartilage.

Perioperative blood loss associated with total knee arthroplasty. A comparison of procedures performed with and without cementing.

We reviewed the cases of thirty-four patients (thirty-eight knees) in whom prostheses with an identical design were used for primary total knee arthroplasty, and we compared the perioperative blood loss between the eleven knees in which cement was used and the twenty-seven knees in which cement was not used. The patients who had an uncemented prosthesis had a significantly greater mean blood loss, both intraoperatively (p less than or equal to 0.05) and during each subsequent eight-hour interval on the first postoperative day (p less than or equal to 0.05). The total for the forty-eight-hour postoperative collection also was greater (p less than or equal to 0.01), as was the cumulative loss for the entire study (p less than or equal to 0.01). When patients who had rheumatoid arthritis and osteoarthrosis were considered separately, the results were similar; that is, there was a significantly greater total postoperative blood loss in each of the two groups when cement was not used (p less than or equal to 0.025). A minimum postoperative hemoglobin concentration of ninety-five grams per liter was maintained; a greater percentage of patients (sixteen of twenty-seven) in whom cement was not used needed a transfusion as compared with two of eleven in the group in whom cement was not used (p less than or equal to 0.025), and they also needed more packed red-blood cells (1062 compared with 750 milliliters) (p less than or equal to 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Development of a prosthetic intervertebral disc.

This article is a preliminary report of a 10-year investigation of the development of an intervertebral disc prosthesis. Spinal fusion is a method for the treatment of chronic, disabling low-back pain that does not respond to nonoperative treatments. Spinal fusion, however, has various adverse effects, and the results of spinal fusion are often unpredictable. The goal of this research project was to develop disc prostheses that have mechanical properties very similar to those of natural, normal discs. Two types of disc prosthesis, one with fiber-reinforced polyurethane and the other with multicomponent, non-fiber-reinforced polymers (C-Flex), have been designed and manufactured. The fiber-reinforced disc was made of polyurethane end-plates with A100 hardness, a homogenous nucleus with A40, and 12 layers of multidirectional (0, +45°), fiber-reinforced anulus with A40 polyurethane. The design and modeling of the multicomponent polymers (non-fiber-reinforced) was made of C-Flex endplates with A90 hardness, a nucleus with A35 occupying 35% of the volume, and an anulus with 70A. Mechanical testing of these disc prostheses demonstrated similar mechanical properties to those of natural, normal discs.

Osteoconductive Composite Grouts for Orthopedic Use

A composite of HA particulate and calcium sulfate hemihydrate has been developed. When this dry material is mixed with either sterile saline or water, the resulting mixture begins to gel. While in the gel or dough state, the composite can be manually inserted or injected under pressure into a bone defect where it sets in situ. The calcium sulfate acts as a binder to hold the HA particles in place. The subsequent resorption of the calcium sulfate leaves controlled porosity for bone ingrowth and attachment to the nonresorbable HA particulate. The combination of calcium sulfate and HA results in a composite with handling properties superior to those of HA alone. Calcium sulfate has a long history of medical use as an implant material. The biocompatibility of the material has been clearly established. The combination of HA and calcium sulfate is likewise extremely compatible as demonstrated in the present studies. Bone ingrowth concomitant with resorption occurs rapidly with efficient conduction of bone from particle to particle. Based on the experiments presented herein, the composite of HA and calcium sulfate may be a useful alternative or adjunct to autogenous bone grafting. Many questions, however, remain regarding long-term tissue response and bone remodeling as well as the efficacy of this material relative to bone grafting.

Mechanical behavior of articular cartilage: Quantitative changes with alteration of ionic environment

Abstract The in vitro viscoelastic mechanical response of normal rabbit articular cartilage is quantitatively altered by changes in the ionic concentration of the test environment. Experimental results indicate that specific functional relationships exist between shear moduli, retardation time spectra and ionic concentration. The forms of these relationships are consistent with the structure and physio-chemical composition of the tissue.

Long-Term Follow-up of Achilles Tendon Repair with an Absorbable Polymer Carbon Fiber Composite

In this cooperative multicenter study for surgical repair of Achilles tendon rupture using a composite implant, 48 patients underwent 52 procedures. This implant is composed of filamentous uniaxially aligned carbon fibers coated with an absorbable polymer. This highly biocompatible implant acts as a scaffold for regrowth of collagenous tissue. The early strength of this repair is provided by the composite implant and by the rapid ingrowth and attachment of new tissue, which allows for an earlier and more vigorous rehabilitation program. Patients with a minimum follow-up of 1 year form the basis of this article. The overall average follow-up is 2.1 years. Three cohort groups were observed on a temporal basis and quantitatively evaluated at 1 year (N = 29), 18 months (N = 22), and 2 years (N = 20), respectively. These three groups demonstrated continuous improvement during the first postoperative year. A high level of function was maintained throughout the second year. Repair of chronic injuries (N = 15) was compared with repair of acute injuries (N = 12) at 1 year following surgery. Both groups greatly improved. However, the acute group had more serious preoperative deficits but improved to a slightly better overall level. Of the patients having at least 1 year follow-up, 86% had a good or excellent result. There was no increased morbidity associated with the use of the carbon implant.

The Mechanical Properties of the Canine Lumbar disc and Motion Segment

A study was initiated to measure the mechanical properties of the canine lumbar spine disc and motion segment at two specific levels. Compressive stiffness was determined to be 717.8 N/mm at L2–3 and 949.0 N/mm at L5–6. Torsional stiffness was found to be 1.04 Nm/deg at L2–3 and 1.72 Nm/deg at L5–6. These data were then compared to human lumbar spine disc and motion segment properties that have been reported in the literature. After normalizing for size differences, the canine lumbar disc showed a similar axial modulus (14.03 MPa for L2–3 and 16.30 MPa for L5–6) and a significantly higher torsional modulus (30.80 MPa for L2–3 and 26.17 MPa for L5–6) when compared to human values. The relative contributions of ligaments, posterior elements, and intervertebral disc to overall stability of the motion segment was found to be similar in canines and humans. As has been shown in human spine research, the posterior elements including the facet joints were found to be significant structures in providing torsional rigidity of the canine spine.

Long-term effects of chondrocyte death on rabbit articular cartilage in vivo

The effects of freezing localized areas of rabbit articular cartilage in vivo were studied at two to twelve months morphologically (gross and microscopic examination, including scanning electron microscopy), histochemically (toluidine blue and safranin O), and metabolically (35S uptake). Up to six months the frozen cartilage was intact but appeared to be dead, as shown by the absence of stainable chondrocytes, severely decreased acid mucopolysaccharide content, and absence of significant uptake of 35S. At twelve months fibrillation and softening were evident, clusters of new chondrocytes with surrounding acid mucopolysaccharides were visible microscopically, and scanning electron microscopy revealed an irregular pattern of collagen fibers which were larger than normal, of varying thickness, and broken in some areas. These changes resembled those seen in degenerative joint disease.

Achilles Tendon Repair with an Absorbable Polymer-Carbon Fiber Composite:

Twenty-seven patients were surgically treated for Achilles tendon rupture using a composite implant. The implant is ribbon-like in configuration and composed of filamentous carbon fiber coated with an absorbable polymer. When used to secure an Achilles repair, the implant acts as a scaffold for the regrowth of collagenous tissue. Rapid attachment of host tissue assures good, early repair strengths which allows for a more vigorous rehabilitation program. Fourteen patients have at least 9 months of follow-up (average follow-up, 14.4 months) and have been objectively and subjectively evaluated on a temporal basis for return of function. To date, complications have been minimal. Results have been very encouraging with 90% return of function at 18 months.

Mechanical and histological studies of acute joint hemorrhage.

In this study, a simple animal model has been used to gather data on the mechanical and histologic changes in cartilage and the histologic changes in synovium attendant to acute joint hemorrhage. The continuous presence of autologous blood in the experimental joints for 10 days results in cartilage which is significantly more compliant than normal. These changes are attributed to loss of proteoglycan. Further, the study demonstrates a consistent pathology of the synovial tissues. Elaboration of degenerative enzymes from iron-laden synovial or subsynovial macrophages must be considered a primary mechanism of cartilage damage.