David H. Sonnabend

Structural Properties of the Intact and the Reconstructed Coracoclavicular Ligament Complex

Numerous procedures have been described for the operative management of acromioclavicular joint injuries, but surprisingly little information is available on the ultimate mechanical behavior of the native coracoclavicular ligament complex or on the various methods of reconstruction. We tested 19 fresh-frozen cadaveric bone-ligament-bone preparations of the coracoclavicular ligament in uniaxial tension at 25 mm/min until failure. Seven specimens were left intact, six had the trapezoid ligament sectioned, and six had the conoid ligament sectioned. Reconstruction of the coracoclavicular ligament was achieved using coracoacromial ligament transfers, woven polyester slings, suture anchors, and Bosworth screws; all reconstructions were also tested to failure. The intact coracoclavicular ligament failed by avulsion or midsubstance tear at 500 (134) N, with a stiffness of 103 (30) N/mm and elongation to failure of 7.7 (1.9) mm. There was no significant difference between the contributions of the conoid or trapezoid ligaments in this loading configuration. Coracoclavicular slings and suture anchors provided strength similar to that of the coracoclavicular ligament, but with significantly greater deformations (14 to 26 mm). Screw fixation resulted in comparable stiffness and superior strength to the coracoclavicular ligament, but only if bicortical purchase was obtained. Coracoacromial ligament transfers were the weakest and least stiff, and augmentation with another form of coracoclavicular fixation is recommended. These results provide a useful baseline for comparison of the initial performance of reconstructive techniques with the performance of the native coracoclavicular ligament.

Proteoglycan 4 downregulation in a sheep meniscectomy model of early osteoarthritis

Osteoarthritis is a disease of multifactorial aetiology characterised by progressive breakdown of articular cartilage. In the early stages of the disease, changes become apparent in the superficial zone of articular cartilage, including fibrillation and fissuring. Normally, a monolayer of lubricating molecules is adsorbed on the surface of cartilage and contributes to the minimal friction and wear properties of synovial joints. Proteoglycan 4 is the lubricating glycoprotein believed to be primarily responsible for this boundary lubrication. Here we have used an established ovine meniscectomy model of osteoarthritis, in which typical degenerative changes are observed in the operated knee joints at three months after surgery, to evaluate alterations in proteoglycan 4 expression and localisation in the early phases of the disease. In normal control joints, proteoglycan 4 was immunolocalised in the superficial zone of cartilage, particularly in those regions of the knee joint covered by a meniscus. After the onset of early osteoarthritis, we demonstrated a loss of cellular proteoglycan 4 immunostaining in degenerative articular cartilage, accompanied by a significant (p < 0.01) decrease in corresponding mRNA levels. Early loss of proteoglycan 4 from the cartilage surface in association with a decrease in its expression by superficial-zone chondrocytes might have a role in the pathogenesis of osteoarthritis.

Morphometric and mechanical evaluation of titanium implant integration: Comparison of five surface structures

Achieving a stable bone-implant interface is an important factor in the long-term outcome of joint arthroplasty. In this study, we employed an ovine bicortical model to compare the bone-healing response to five different surfaces on titanium alloy implants: grit blasted (GB), grit blasted plus hydroxyapatite (50 microm thick) coating (GBHA), Porocoat(R) (PC), Porocoat(R) with HA (PCHA) and smooth (S). Push-out testing, histology, and backscatter scanning electron microscope (SEM) imaging were employed to assess the healing response at 4, 8, and 12 weeks. Push-out testing revealed PC and PCHA surfaces resulted in significantly greater mechanical fixation over all other implant types at all time points (p <.05). HA coating on the grit-blasted surface significantly improved fixation at 8 and 12 weeks (p <.05). The addition of HA onto the porous coating did not significantly improve fixation in this model. Quantification of ingrowth/ongrowth from SEM images revealed that HA coating of the grit-blasted surfaces resulted in significantly more ongrowth at 4 weeks (p <.05).

Resurfacing of the glenoid in total shoulder arthroplasty : A comparison, at a mean of five years, of prostheses inserted with and without cement

BACKGROUND Clinically evident loosening of a glenoid component inserted with cement in total shoulder arthroplasty is infrequent, but radiographic changes that indicate loosening at the implant-bone interface are common and have been associated with functional limitation. We compared the results of total shoulder arthroplasties in which the glenoid implant had been inserted with cement with those of arthroplasties in which a bone-ingrowth glenoid implant had been inserted without cement. METHODS The results of eighty-six consecutive total shoulder arthroplasties, performed by the same surgeon, were retrospectively reviewed between four and seven years after the operation. Fifty-eight shoulders in which the primary glenoid implant was in situ were assessed with use of the Simple Shoulder Test and Short Form-36 questionnaires, clinical examination, and fluoroscopic imaging of the glenoid implant-bone interface. Thirty-two of the glenoid components had been fixed with cement and twenty-six, without cement. RESULTS Complications occurred in 16 percent (fourteen) of the eighty-six shoulders, and 9 percent (eight) of the shoulders needed a revision operation. None of the revisions were done because of loosening of the glenoid component. Five of the eight revisions involved implants that had been inserted without cement. Three of these implants were revised because of early instability and two, because the polyethylene component had separated from the metal tray of the glenoid implant. With the numbers available, we could not detect any significant differences between the groups with respect to pain, range of motion, function of the shoulder, or general health. Radiographic analysis demonstrated a high level of interobserver agreement (kappa = 0.89). Radiolucent lines were observed after 41 percent (thirteen) of the thirty-two arthroplasties performed with cement compared with 23 percent (six) of the twenty-six arthroplasties performed without cement. The proportion of implants classified as probably loose was approximately three times greater in the group in which cement had been used. Eccentric wear of the posterior rim of the metal tray and focal osteolysis under the metal tray were observed in the group in which the component had been inserted without cement; these findings may indicate a potential for progression of radiographic loosening with increased durations of follow-up. CONCLUSIONS We concluded that, despite the higher rate of early complications, the intermediate-term outcomes of arthroplasties in which the glenoid implant is inserted without cement are comparable with those of arthroplasties with cementing of the glenoid component.

Fracture healing in a rat osteopenia model.

Fracture healing is influenced by mechanical and biologic factors. The capacity for fracture repair has been reported to decrease with age, although the risk of fracture increases with age. Fracture healing in an animal model of postmenopausal osteoporosis or osteopenia would provide a useful technique to evaluate and develop new treatment protocols. The authors examined the tensile and bending properties of healing femoral fractures in normal and ovariectomized rats. Mechanical data from tensile and bending tests indicate ovariectomy impairs fracture healing, which was confirmed through histologic study. Bending and tensile data provide useful information concerning the mechanical properties of the healing fracture. Tensile tests were noted to be sensitive indicators of the properties of the healing fracture.

Type 2 fractures of the distal clavicle: A new surgical technique

Neer type 2 fractures of the distal clavicle have a high rate of nonunion and delayed union. In this series nine cases of coracoclavicular ligament reconstruction with Dacron graft material led to union at the fracture site. All patients had no symptoms and returned to full activity. This technique allows for stable fixation with early mobilization and return to work and sports.

Modulation of aggrecan and ADAMTS expression in ovine tendinopathy induced by altered strain

OBJECTIVE To evaluate histologic, immunohistochemical, and molecular changes in tendon induced by altered strain in a large-animal model. METHODS A full-thickness partial-width laceration of the infraspinatus tendon was created in 5 sheep, while 5 sham-operated sheep were used as controls. Sheep were killed after 4 weeks, and 4 differentially stressed tendon regions (tensile or near bone attachment from overstressed or stress-deprived halves) were evaluated for histopathology, proteoglycan (PG) accumulation, and characterization of glycosaminoglycans and aggrecan catabolites. Gene expression of matrix components, enzymes, and inhibitors was analyzed by reverse transcriptase-polymerase chain reaction. RESULTS Histopathologic changes were detected in both overstressed and stress-deprived tensile tendon, but only in stress-deprived tendon near bone. In overstressed and stress-deprived tensile tendon, levels of keratan sulfate, chondroitin 4-sulfate, and chondroitin 6-sulfate were increased. In overstressed tensile tendon, levels of ADAMTS-generated aggrecan catabolites were increased. There was increased matrix metalloproteinase 13 (MMP-13) and decreased fibromodulin and decorin expression in all regions. Increased MMP-1, MMP-9, MMP-14, and ADAMTS-1 expression, and decreased type II collagen expression were restricted to stress-deprived tendon. In stress-deprived bone-attachment regions, messenger RNA (mRNA) for aggrecan was decreased, and ADAMTS was increased. In overstressed tensile tendon, aggrecan mRNA was increased, and ADAMTS was decreased. CONCLUSION The distinct molecular changes in adjacent tissue implicate altered strain rather than humoral factors in controlling abnormal tenocyte metabolism, and highlight the importance of regional sampling. Tendon abnormalities induced by increased strain are accompanied by increased aggrecan, decreased ADAMTS, and low PG expression, which may negatively impact the structural integrity of the tissue and predispose to rupture.

Regional assessment of articular cartilage gene expression and small proteoglycan metabolism in an animal model of osteoarthritis

Osteoarthritis (OA), the commonest form of arthritis and a major cause of morbidity, is characterized by progressive degeneration of the articular cartilage. Along with increased production and activation of degradative enzymes, altered synthesis of cartilage matrix molecules and growth factors by resident chondrocytes is believed to play a central role in this pathological process. We used an ovine meniscectomy model of OA to evaluate changes in chondrocyte expression of types I, II and III collagen; aggrecan; the small leucine-rich proteoglycans (SLRPs) biglycan, decorin, lumican and fibromodulin; transforming growth factor-β; and connective tissue growth factor. Changes were evaluated separately in the medial and lateral tibial plateaux, and were confirmed for selected molecules using immunohistochemistry and Western blotting. Significant changes in mRNA levels were confined to the lateral compartment, where active cartilage degeneration was observed. In this region there was significant upregulation in expession of types I, II and III collagen, aggrecan, biglycan and lumican, concomitant with downregulation of decorin and connective tissue growth factor. The increases in type I and III collagen mRNA were accompanied by increased immunostaining for these proteins in cartilage. The upregulated lumican expression in degenerative cartilage was associated with increased lumican core protein deficient in keratan sulphate side-chains. Furthermore, there was evidence of significant fragmentation of SLRPs in both normal and arthritic tissue, with specific catabolites of biglycan and fibromodulin identified only in the cartilage from meniscectomized joints. This study highlights the focal nature of the degenerative changes that occur in OA cartilage and suggests that altered synthesis and proteolysis of SLRPs may play an important role in cartilage destruction in arthritis.

Mechanical and histologic evaluation of Collagraft in an ovine lumbar fusion model

The purpose of this study was to determine the effectiveness of a composite material composed of Type I bovine dermal collagen, 65% hydroxyapatite, and 35% tricalcium phosphate ceramic (Collagraft Bone Graft Matrix Strip NeuColl Incorporated, Palo Alto, CA) as a bone graft substitute for spinal fusion with and without the use of autologous bone marrow in an ovine lumbar spine model with pedicle screw fixation. Twenty-four adult sheep underwent a single level posterolateral (intertransverse process) L3-L4 lumbar fusion with one of three graft materials combined with rigid pedicle screw fixation. The three graft materials were Collagraft, Collagraft with marrow, and autogenous corticocancellous bone graft. Animals were euthanized 6 months after surgery and evaluated using dual energy xray absorptiometry, radiographs, histologic analysis, and mechanical testing. Dual energy xray absorptiometry between the transverse processes revealed that the mineral densities for the two Collagraft groups were significantly higher than the autogenous bone graft group. Histologic analysis confirmed that Collagraft was highly compatible and was well incorporated into the fusion mass. Both Collagraft groups had thick trabeculae and a mixture of lamellar and plexiform bone. The autogenous bone graft group had a smaller fusion complex, composed primarily of lamellar bone with thinner and fewer trabeculae. All three groups had similar mechanical properties. These results support the use of Collagraft in spinal fusion with pedicle screw fixation.

Semitubular blade plate fixation in proximal humeral fractures: A biomechanical study in a cadaveric model

This study was undertaken to compare the fixation of the semitubular blade plate with that of the AO T plate. Cadaveric humeri (n=12 pairs) from an elderly population (41 to 89 years) had either a blade plate (n=12) or a T plate (n=12) fixed to them, subsequent to which a transverse osteotomy was performed. Mechanical testing in tension was performed in 1 series (n=5, blade plate; n=5, T plate) by applying a single maximal load to failure and in a second series (n=7, blade plate; n=7, T plate) by applying submaximal cyclic loading before failure was induced. Results showed that the fixation provided by the semitubular blade plate was significantly better (P < .05) than that of the T plate in those specimens subjected to submaximal cyclic loading before failure (series 2). This latter testing method contains some component of the clinical situation compared with monotonic distraction to failure. Based on these results plus favorable clinical results reported in the literature, the semitubular blade plate is possibly a better alternative to the T plate in the management of proximal humeral fractures that require open reduction and internal fixation.