Michael G. Ehrlich

RGD-coated titanium implants stimulate increased bone formation in vivo

Numerous studies have demonstrated that peptide modified surfaces influence short- and long-term cell responses such as attachment, shape and function in vitro. These responses are mediated via cell receptors known as integrins which bind specifically to short peptide sequences from larger proteins. Integrins transduce information to the nucleus through several cytoplasmic signalling pathways. Little is known, however, about the ability of peptide-coated surfaces to influence cell responses in vivo. The present study was designed to evaluate the quality and quantity of the new bone formed in response to titanium rods surface-coated with the peptide sequence Arg-Gly-Asp-Cys (RGDC) using gold-thiol chemistry and implanted in rat femurs. Histomorphometric analysis of cross-sections perpendicular to the implant long axis showed a significantly thicker shell of new bone formed around RGD-modified versus plain implants at 2 weeks (26.2 +/- 1.9 vs. 20.5 +/- 2.9 microm; P < 0.01). A significant increase in bone thickness for RGD implants was also observed at 4 weeks while bone surrounding controls did not change significantly in thickness (32.7 +/- 4.6 vs. 22.6 +/- 4.0 microm; P < 0.02). Mechanical pull-out testing conducted at 4 weeks revealed the average interfacial shear strength of peptide modified rods was 38% greater than control rods although this difference was not statistically significant. These pilot data suggest that an RGDC peptide coating may enhance titanium rod osseointegration in the rat femur. Long-term studies and evaluation of other peptides in larger animal models are warranted.

Instability of the distal tibiofibular syndesmosis after bimalleolar and trimalleolar ankle fractures.

We studied the late results after bimalleolar and trimalleolar ankle fractures in thirty-four patients after an average follow-up of four years. Twenty-one patients had had open reduction and internal fixation of the medial malleolus only and thirteen, internal fixation of both the medial malleolus and the lateral malleolus. Twenty-four lesions were supination-external rotation fractures; six, pronation-external rotation; and four, supination-adduction fractures. All initial and post-reduction roentgenograms were evaluated, and the patients were re-evaluated two to seven years after fracture. Re-evaluation included physical examination as well as standardized and stress roentgenograms of both ankles. Criteria were developed for measuring the width of the syndesmosis and assessing the late roentgenographic, subjective, and objective results, as well as any late instability of the syndesmosis and osteoarthritis. Significant correlations were found between: (1) the adequacy of the reduction of the syndesmosis and late arthritis, (2) the adequacy of the initial reduction of the syndesmosis and the late stability of the syndesmosis, (3) the late stability of the syndesmosis and the final outcome, and (4) the adequacy of the reduction of the lateral malleolus and that of the syndesmosis. Based on the findings in this small series and on the evidence published in the literature, we concluded that adequate reduction of the syndesmosis is necessary to achieve a stable ankle following supination-external rotation and pronation-external rotation fractures of the ankle, and that the reduction of the syndesmosis will be unsatisfactory if the lateral malleolus is not well reduced.

Effect of repetitive impulsive loading on the knee joints of rabbits.

To simulate the forces from hopping, the right foot of adult rabbits was subjected to 1 1/2 the animals body weight 40 times a minute for 20-40 minutes per day. During these brief periods of repetitive impulsive loading the legs were held in short-leg splints to eliminate the natural shock-absorbing mechanism associated with ankle dorsiflexion and calve muscle stretching. Under these conditions subchondral bone stiffening occurred and was associated with the earliest metabolic changes of cartilage damage. When bone stiffening returned to normal the effect on the cartilage did not completely disappear, although these effects diminished. The results suggested that subchondral bone stiffening accompanies the earliest metabolic changes in osteoarthrosic chondrocytes and suggests that trabecular microfracture may occur very early in this sequence of events.

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.

An experimental model of femoral condylar defect leading to osteoarthrosis

Summary: The acute treatment of articular step-off injuries is based largely on reduction criteria, because the presence of residual incongruity has been correlated with the development of posttraumatic arthrosis (PTA). However, this association has not been demonstrated on a prospective basis. Using the rabbit femoral condyle, we developed a surgical model of articular condylar defect without sacrificing the axial alignment or inherent stability of the knee joint. Twenty weeks after the creation of 5-mm femoral condylar defects, progressive osteoarthritic changes were confirmed by radiographic, histological, and biochemical parameters. Osteophytes were observed on the medial aspect of operated knee joints in 67% of cases. Femoral and tibial articular cartilage at the site of the condylar defect exhibited fibrillation, hypocellularity, and severe loss of safranin-0 staining. Focal areas of cartilage were denuded or replaced by pannus. In no case was femoral congruity restored by cartilage repair. Statistically significant decreases in proteoglycan content were demonstrated for cartilage sampled from the weight-bearing region of the condylar defect and from the tibial surface directly beneath it. These changes resemble those arising from previously reported models of osteoarthrosis. We present the model as a valid tool for the study of articular condylar defect and its role in the development of PTA.

Collagenase and collagenase inhibitors in osteoarthritic and normal cartilage.

In advanced osteoarthritis, all of the cartilaginous components are lost from the joint surface. Although mechanisms exist for proteoglycan degradation, there is not known to be any system for removal of the collagen. This study suggests that the loss of the collagen components may be a function of articular cartilage collagenase. The enzyme in normal human cartilage is bound to an inhibitor and appears to be present in very small amounts. Attempts to demonstrate collagenase activity in ground human articular cartilage or in its lysosomal fraction were unsuccessful. 7-Day cartilage tissue cultures also failed to demonstrate the presence of the enzyme; but the same culture fluid, incubated with trypsin, showed significant degradation of collagen, suggesting that trypsin destroyed the inhibitor. 7-Day culture fluids were then chromatographed on a heparin-charged Sepharose 4B affinity column that had been activated with cyanogen bromide. This removed the inhibitor, and the chromatographed fluid from osteoarthritic cartilage released 42% of the incorporated counts of the collagen substrate, whereas normal cartilage released 10.1% and a trypsin control, 6.4%. Electrophoresis of the degradation products of the enzyme-collagen complex incubated at 37 degrees C revealed breakdown was complete to small dialyzable fragments, while at 25 degrees C larger fragments were split off.

Ptpn11 deletion in a novel progenitor causes metachondromatosis by inducing hedgehog signalling.

The tyrosine phosphatase SHP2, encoded by PTPN11, is required for the survival, proliferation and differentiation of various cell types. Germline activating mutations in PTPN11 cause Noonan syndrome, whereas somatic PTPN11 mutations cause childhood myeloproliferative disease and contribute to some solid tumours. Recently, heterozygous inactivating mutations in PTPN11 were found in metachondromatosis, a rare inherited disorder featuring multiple exostoses, enchondromas, joint destruction and bony deformities. The detailed pathogenesis of this disorder has remained unclear. Here we use a conditional knockout (floxed) Ptpn11 allele (Ptpn11fl) and Cre recombinase transgenic mice to delete Ptpn11 specifically in monocytes, macrophages and osteoclasts (lysozyme M-Cre; LysMCre) or in cathepsin K (Ctsk)-expressing cells, previously thought to be osteoclasts. LysMCre;Ptpn11fl/fl mice had mild osteopetrosis. Notably, however, CtskCre;Ptpn11fl/fl mice developed features very similar to metachondromatosis. Lineage tracing revealed a novel population of CtskCre-expressing cells in the perichondrial groove of Ranvier that display markers and functional properties consistent with mesenchymal progenitors. Chondroid neoplasms arise from these cells and show decreased extracellular signal-regulated kinase (ERK) pathway activation, increased Indian hedgehog (Ihh) and parathyroid hormone-related protein (Pthrp, also known as Pthlh) expression and excessive proliferation. Shp2-deficient chondroprogenitors had decreased fibroblast growth factor-evoked ERK activation and enhanced Ihh and Pthrp expression, whereas fibroblast growth factor receptor (FGFR) or mitogen-activated protein kinase kinase (MEK) inhibitor treatment of chondroid cells increased Ihh and Pthrp expression. Importantly, smoothened inhibitor treatment ameliorated metachondromatosis features in CtskCre;Ptpn11fl/fl mice. Thus, in contrast to its pro-oncogenic role in haematopoietic and epithelial cells, Ptpn11 is a tumour suppressor in cartilage, acting through a FGFR/MEK/ERK-dependent pathway in a novel progenitor cell population to prevent excessive Ihh production.

Knee Laxity Does Not Vary With the Menstrual Cycle, Before or After Exercise

Background An intriguing explanation for the disproportionately high rate of anterior cruciate ligament injury in female athletes is that the structural properties of the anterior cruciate ligament are affected by the menstrual hormones. Whether this actually occurs, however, is the subject of ongoing debate. Hypotheses (1) Anterior cruciate ligament laxity is different in the follicular, ovulatory, and luteal phases of the menstrual cycle, and (2) exercise exacerbates the difference in anterior cruciate ligament laxity in the 3 phases. Methods Over the course of 10 weeks, repeated knee laxity measurements were taken on 27 high-level female athletes, before and after exercise. Point in the menstrual cycle was determined with charts of waking temperature and menstruation. The independent effects of menstrual phase and exercise were evaluated using generalized estimating equations. Results Data from 18 participants were included in the final analysis. There were no significant differences in anterior cruciate ligament laxity in any of the 3 menstrual phases, before or after exercise. Conclusions Anterior cruciate ligament laxity is not significantly different during the follicular, ovulatory, and luteal phases of the menstrual cycle, and bicycling exercise does not exacerbate or create any differences in anterior cruciate ligament laxity.

Effects of local injection of corticosteroids on the healing of ligaments. A follow-up report.

One hundred and one skeletally mature New Zealand White rabbits were used to study the long-term effects of a single injection of corticosteroid on the biomechanical, histological, and biochemical properties of ligament-healing. Two steroid doses were studied, as previously described. The injections were made into a fascial pocket immediately after transection of the ligament. The animals were killed forty-two and eighty-four days after the injury. In our previous investigation, in which we examined the early (inflammatory and proliferative) phases of ligament-healing, the specimens that had been injected with a dose of steroids equivalent to that given to humans demonstrated significantly inferior biomechanical properties and histological organization relative to controls that had not received an injection. In the current study, we examined the later (remodeling and maturation) phases of ligament-healing and found that the tensile strength (the ultimate stress) of the specimens that had been injected with the steroids returned to a value that was equal to that of the controls that had not received an injection; however, the peak load of the specimens that had been injected with steroids remained inferior to that of the controls. This was accompanied by a lag in the histological maturation.

Healing Characteristics of a Type I Collagenous Structure Treated with Corticosteroids

One hundred twenty-eight skeletally mature New Zea land White rabbits were used to study the effect of a single corticosteroid injection on the biomechanical, biochemical, and histologic aspects of ligamentous healing. Two steroid dosages were used. The amount of the low-dose steroid was calculated by determining the corticosteroid concentration at which fibroblastic synthesis of collagen was inhibited in vitro. A human equivalent dose of betamethasone was used as the high-dose steroid injection. These two steroid doses and a saline control were injected around a transected medial collateral-ligament. At 10 days all groups showed significantly inferior biomechanical properties relative to noninjected controls. By 3 weeks the human equivalent steroid dose group continued to demonstrate signifi cantly inferior properties. Histologic and biochemical analyses confirmed the biomechanical results. The clinical relevance of the study was that the delivery of a human equivalent steroid dose into an acutely injured ligament significantly impairs the healing process rela tive to a noninjected ligament at 10 days and at 3 weeks after injury. This implies that a corticosteroid-treated in jured ligament may not be able to withstand the me chanical loads of early vigorous rehabilitation.