David J. Zaleske

Recapitulation of signals regulating embryonic bone formation during postnatal growth and in fracture repair

A number of proteins have recently been identified which play roles in regulating bone development. One important example is Indian hedgehog (Ihh) which is secreted by the prehyprtrophic chondrocytes. Ihh acts as an activator of a second secreted factor, parathyroid hormone-related protein (PTHrP), which, in turn, negatively regulates the rate of chondrocyte differentiation. Here we examine the expression of these genes and their molecular targets during different stages of bone development. In addition to regulating PTHrP expression in the perichondrium, we find evidence that Ihh may also act on the chondrocytes themselves at particular stages. As bone growth continues postnatally in mammals and the developmental process is reactivated during fracture repair, understanding the molecular basis regulating bone development is of medical relevance. We find that the same molecules that regulate embryonic endochondral ossification are also expressed during postnatal bone growth and fracture healing, suggesting that these processes are controlled by similar mechanisms.

Cell-Based Therapy for Meniscal Repair A Large Animal Study

Background The avascular portion of the meniscus cartilage in the knee does not have the ability to repair spontaneously. Hypothesis Cell-based therapy is able to repair a lesion in the swine meniscus. Study Design Controlled laboratory study. Methods Sixteen Yorkshire pigs were divided into four groups. A longitudinal tear was produced in the avascular portion of the left medial meniscus of 4 pigs. Autologous chondrocytes were seeded onto devitalized allogenic meniscal slices and were secured inside the lesion with two sutures. Identical incisions were created in 12 other pigs, which were used as three separate control groups: 4 animals treated with an unseeded scaffold, 4 were simply sutured, and 4 were left untreated. Meniscal samples were collected after 9 weeks, and the samples were analyzed grossly, histologically, and histomorphometrically. Results Gross results showed bonding of the lesion margins in the specimens of the experimental group, whereas no repair was noted in any of the control group specimens. Histological and histomorphometrical analysis showed multiple areas of healing in the specimens of the experimental group. Conclusions This study demonstrated the ability of seeded chondrocytes to heal a meniscal tear. Clinical Relevance Cell-based therapy could be a potential tool for avascular meniscus repair.

Effects of hyaluronan on engineered articular cartilage extracellular matrix gene expression in 3-dimensional collagen scaffolds.

Hyaluronan (HA) is a component of cartilage matrix with known effects on chondrocytes. We tested the effects of adding HA to 3-dimensional (3-D) collagen. sponges on chondrocyte function in vitro. Bovine articular chondrocytes isolated by collagenase digestion were injected into either collagen or HA/collagen scaffolds comprising different amounts of HA (2, 5, 10, and 14% w/w). Expression of aggrecan and type II collagen genes was measured by gene-specific quantitative competitive reverse transcriptase-polymerase chain reactions, and the extracellular matrix was estimated by histomorphometrical analyses. After 7-day culture, the chondrocytes in 2% (w/w) HA sponges expressed fourfold more mRNA transcripts for type II collagen (p = 0.002) and twofold more mRNA transcripts for aggrecan (p = 0.022) than in control collagen sponges. Furthermore, there was 45% more extracellular matrix in 2% (w/w) HA sponges and 43% less matrix in the 10% (w/w) HA sponges compared with plain collagen sponges (p > 0.05). In sum, a small amount of HA in 3-D collagen scaffolds enhanced chondrogenesis, but a greater amount was inhibitory. This 3-D system represents a novel tool to identify mechanisms by which extracellular matrix molecules influence chondrocyte function. Further, these results show the potential for modifying scaffolds to improve production of engineered cartilage for in vivo applications.

Meniscal repair using engineered tissue

In this study, devitalized meniscal tissue pre‐seeded with viable cultured chondrocytes was used to repair a bucket‐handle incision in meniscal tissue transplanted to nude mice. Lamb knee menisci were devitalized by cyclic freezing and thawing. Chips measuring four by two by one‐half millimeters were cut from this devitalized tissue to serve as scaffolds. These chips were then cultured either with or without viable allogeneic lamb chondrocytes. From the inner third of the devitalized meniscal tissue, rectangles were also cut approximately 8 × 6 mm. A 4 mm bucket‐handle type incision was made in these blocks. The previously prepared chips either with (experimental group) or without viable chondrocytes (control group) were positioned into the incisions and secured with suture. Further control groups included blocks of devitalized menisci with incisions into which no chips were positioned and either closed with suture or left open with no suture. Specimens were transplanted to subcutaneous pouches of nude mice for 14 weeks. After 14 weeks, seven of eight experimental specimens (chips with viable chondrocytes) demonstrated bridging of the incision assessed by gross inspection and manual distraction. All the control groups were markedly different from the experimental group in that the incision remained grossly visible. Histological analysis was consistent with the differences apparent at the gross level. Only the experimental specimens (chips with viable chondrocytes) with gross bridging demonstrated obliteration of the interface between incision and scaffold. None of the control specimens revealed any cells or tissue filling the incision. Tissue engineering using scaffolds and viable cells may have an application in meniscal repair in vivo.

Vascular events associated with the appearance of the secondary center of ossification in the murine distal femoral epiphysis.

Although the formation of a secondary center of ossification is often compared with that of the primary center, there are striking differences between these processes. In the formation of the primary center, vascular invasion is always associated with the maturation of chondrocytes, whereas vascularization of the epiphysis can proceed in two different ways. In some species, the epiphysis is vascularized by cartilage canals before the appearance of the secondary center. However, in the mouse, the distal femoral epiphysis is vascularized by peripheral vascular invasion without pre-existing cartilage canals. Histological study of serial sections and studies of vascularization by injection with India ink demonstrated the relationship between hypertrophic chondrocyte formation, vascular invasion, and the formation of the secondary center of ossification in the murine distal femoral epiphysis.

Heterotopic Ossification Around the Elbow Following Burns in Children: Results After Excision

BACKGROUND Major burn injuries close to joints alter the function of the musculoskeletal system through tissue loss and limitation of joint motion. In children with involvement of the hand, wrist, and forearm, restriction of elbow motion secondary to heterotopic ossification following a burn injury severely limits the function of the upper extremity. The purpose of this study was to review elbow function following excision of heterotopic ossification around the elbow in children. METHODS Eight children (ten elbows) from a population of 3245 consecutive patients who were admitted to our pediatric burn center were found to have severe heterotopic ossification of the elbow, leading to an inability to reach the mouth for feeding and the head and the perineum for self-care. Excision of the heterotopic ossification was undertaken if the patient had this limitation of function and if movement was restricted to a total arc of motion of <50 degrees. Pain was not an indication for the operation. The procedure was performed at an average of 17.3 months following the injury. RESULTS Seven children (nine elbows) were available for follow-up at an average of fifty-six months after surgery. All nine elbows had an improved arc of motion (an average increase of 57 degrees ). Following excision, heterotopic ossification did not recur. All children were able to reach the face and the perineum following the operation. CONCLUSIONS Excision of heterotopic ossification around the elbow following a burn injury in children can improve the arc of motion and improve the function of the extremity. A relatively simple operative and postoperative regimen can achieve satisfactory results.

Brace treatment for symptomatic spondylolisthesis.

The literature documents progression of spondylolisthesis, most commonly during the adolescent growth spurt. Twenty-eight patients with Grades I and II spondylolisthesis were treated with antilordotic braces. Presenting signs and symptoms included back pain (61%), tight hamstrings (53%), increased lordosis (25%), and mild scoliosis (21%). Three patients presented with spondylolysis and progressed to a slip prior to initiation of brace treatment. Mean duration of brace treatment was 25 months. In the brace, lateral roentgenograms demonstrated a significant reduction of lumbar lordosis and sacral inclination. At the conclusion of brace treatment all patients were pain-free and none had demonstrated a significant increase in slip percent.

Extremity lawn-mower injuries in children : Report by the Research Committee of the Pediatric Orthopaedic Society of North America

In a multicenter study of pediatric lawn-mower injuries (push or riding gas-powered machines), we reviewed 144 children at an average age of injury of 7.0 years; 77% were boys. Most injuries (92 of 104) occurred in the afternoon. The child was the machine operator in 36 cases, a bystander in 84, and a passenger in 21. The average hospital stay was 13.3 days with 2.6 surgeries per child. Amputations occurred in 67 children; 63 were unilateral and four bilateral; the most common level was the toes (63%). Blood transfusions were given to 35 children. Children injured by riding lawn mowers, when compared with those by push lawn mowers, were younger (5.4 vs. 11.0 years), less frequently the operator (15 vs. 60%), had longer hospitalizations (15.0 vs. 8.9 days), and required more surgeries (3.0 vs. 1.6) and blood transfusions (41 vs. 3%). Children with free flaps needed more transfusions (78 vs. 26%), and transfused children were younger (4.6 vs. 8.1 years), more likely to be bystanders (91 vs. 63%), required more surgeries (4.1 vs. 2.0), and were hospitalized longer (21.6 vs. 9.7 days). Soft-tissue infections occurred in eight of 118 and osteomyelitis occurred in six of 117 children. At an average follow-up of 1.9 years, there were 43 satisfactory and 84 unsatisfactory results. When excluding those children with amputations of digits, there were 42 satisfactory and 47 unsatisfactory results. If children younger than 14 years had not been permitted around lawn mowers, approximately 85% of the injuries in this report would have been prevented. Further public dissemination of the following information is needed: (a) children younger than 14 years should not operate lawn mowers, (b) children younger than 14 years should not be in the yard while the lawn is being mowed, and (c) no passengers, regardless of age, should be allowed on riding mowers.

Analyzing forearm fractures in children. The more subtle signs of impending problems.

Poor results with pediatric forearm fractures, while infrequent, do occur. Systematic analysis is required to identify this relatively rare, evolving problem. The purpose of this retrospective study was to identify and organize factors that would help in this process. Sixty-nine patients aged one-17 years with displaced forearm fractures were identified retrospectively. Pre- and postreduction radiographs were analyzed in comparison to standards for displacement, angulation, bow, shortening, and rotation. Those patients who seemed most likely to have problems following treatment were recontacted. Even with the use of stringent criteria in a group weighted toward more severe fractures, 85% of the patients achieved satisfactory results. With careful analysis of fractures for changes in angulation, bow, and disruption of the proximal or distal radioulnar joints, these problems should be avoidable. Analysis relative to standard radiographs aids in the identification of subtle malalignments that would otherwise be easily overlooked.

Congenital intraspinal lipomas: clinical presentation and response to treatment

A retrospective review of 29 patients with surgically treated intraspinal lipomas was conducted in a determination of their manner of presentation and response to treatment. The average age at the time of diagnosis for the entire group was 12.8 years. Only five patients were neurologically normal by clinical examination at the time of diagnosis, and these five patients were all <6 months old. Orthopedic intervention was judged successful in each of the 11 foot procedures done after surgery on the lipoma, but in only two of the five foot procedures done before such surgery. We conclude that consideration of intraspinal lipoma is worthwhile in several circumstances, including pediatric foot deformities.