Todd C. Battaglia

The effect of growth/differentiation factor-5 deficiency on femoral composition and mechanical behavior in mice

A subclass of the bone morphogenetic proteins (BMPs), known as growth/differentiation factors (GDFs) 5, 6, and 7, have been shown to affect several skeletal processes, including endochondral ossification, synovial joint formation, and tendon and ligament repair. Mice deficient in GDF-5 have also been shown to exhibit biomechanical abnormalities in tendon that may be associated with altered type I collagen. The purpose of this study was to investigate the effect of GDF-5 deficiency on another type I collagen-rich tissue: cortical bone. Analyses were performed on femora from 8-week-old GDF-5-deficient male brachypodism mice. We hypothesized that GDF-5-deficient bones would exhibit altered geometric, structural, and material properties compared with control littermates. Mutant animals were significantly smaller in body mass than controls (-21%). Geometrically, mutant long bones were significantly shorter (-25%), had a lower polar moment of inertia (-34%), and a lower geometric strength indicator (analogous to the section modulus of a circular section) (-30%). When normalized by body mass, however, geometric differences were no longer significant. Structurally, GDF-5-deficient femora were weaker (-31%) and more compliant (-57%) than controls when tested to failure in torsion. Lower bone structural stiffness in the mutants was not completely explained by the smaller bone geometry, because mutant bones exhibited a significantly lower effective shear modulus (-36%). Although body mass did not fully explain the reduced structural strength in mutant bones, strength differences were adequately explained by bone cross-sectional geometry; maximum effective shear stress was not significantly different between mutants and controls, despite a statistically significant 6% lower ash fraction in mutant femora. No significant difference was detected in collagen content, as indicated by hydroxyproline per dry mass.

Semitendinosus Regrowth Biochemical, Ultrastructural, and Physiological Characterization of the Regenerate Tendon

Background Previous studies have suggested that hamstring tendons can regenerate following harvesting for anterior cruciate ligament reconstruction. Hypothesis This “neo-tendon” is a true, functional tendon, not scar tissue. Study Design Controlled laboratory study. Methods Semitendinosus tendons were harvested from 35 New Zealand white rabbits using a standard tendon stripper. The rabbits were sacrificed 9 to 12 months following the index procedure and thoroughly evaluated. Results Thirty-one rabbits were available at the time of sacrifice. The neo-tendon was present in 26 rabbits but was highly variable in size and location of its tibial insertion. Histologic and immunohistochemical staining confirmed that the regenerate tissue was indeed tendon with normal cellularity, organization, and immunolocalization of type I collagen. Electron microscopy showed regeneration of organized collagen tissue that simulated native tendon but with a smaller cross-sectional diameter. Functionally, the neo-tendon was able to transmit force across the musculotendinous junction but at a significantly slower rate than the opposite, control leg. Biomechanical properties of the neo-tendon were significantly less than the control side. Biochemical analysis revealed that the neo-tendons contained glycosaminoglycans and collagen, but levels were significantly lower than normal tendons. Conclusions Semitendinosus tendons regenerate with biologically reactive tendinous tissues in an animal model. This tissue has many of the characteristics of a normal tendon but appears to be inferior to the original musculotendinous unit at 9- to 12-month evaluation. Further characterization of the “lizard tail phenomenon” is still needed. Clinical Relevance Hamstring tendon regrowth may have a dramatic impact on postoperative function of patients who undergo anterior cruciate ligament reconstruction with these tendons. Further modulation of this regeneration may further reduce graft harvesting morbidity.

Ultrastructural Determinants of Murine Achilles Tendon Strength During Healing

The mechanisms by which tendon strength is established during growth and development and restored following injury are not completely understood and are likely to be complex, multifactorial processes. Several studies examining the relationship between mechanical behavior and ultrastructural characteristics of tendons and ligaments during growth and maturation suggest that collagen fibril diameter is strongly correlated with tendon strength. Because of the similarities between development and repair processes of musculoskeletal tissues, increases in tendon strength during healing may be related to increases in fibril ultrastructural parameters such as fibril size, numerical density, and area fraction. In this study, we compared murine Achilles tendons at various time points after tenotomy with sham-operated controls in tensile tests to failure and examined tendons using electron microscopy to assess collagen fibril ultrastructure. We found that in the 6-week period following Achilles tenotomy, fibril mean diameter remained significantly smaller than sham-side diameter by a factor of 2–3. Despite the persistently small fibril size, increasing numerical density resulted in a gradual increase in fibril area fraction. Biomechanical strength did not reach that of intact tendons until some time between 5 and 7 weeks, approximately the same time period when fibril area fraction began to approach sham values. These data suggest that parameters other than collagen fibril size are most responsible for increased tendon strength during healing.

Traumatic hemipelvectomy: case report and literature review

Traumatic hemipelvectomy is a rare but devastating injury involving complete disruption of the hemipelvis from the pubic symphysis to the sacroiliac joints and often results in death. We present an interesting case of traumatic hemipelvectomy caused by a previously undescribed mechanism of injury in which judicious angiography and aggressive surgical treatment contributed to patient survival.

Rotator Cuff Tear in a 13-Year-Old Baseball Player A Case Report

Rotator cuff injuries are among the most common shoulder injuries seen in athletes. They occur mostly in baseball players and other athletes who frequently use the arm in overhead or throwing positions. Although juvenile and adolescent baseball players are also prone to shoulder injuries, tears of the rotator cuff are extremely uncommon in this age group. A review of the orthopaedic and sports medicine literature found no reports specific to rotator cuff injuries in adolescents. In addition, among the numerous studies focusing on treatment of rotator cuff injuries in young athletes, the youngest patient included in any report was 18 years old. We describe the repair of a high-grade partial-thickness tear of the supraspinatus tendon that occurred in a 13-year-old baseball pitcher.

Geometric and Material Contributions to Whole Bone Structural Behavior in GDF-7-Deficient Mice

The growth/differentiation factors (GDFs) are a subfamily of bone morphogenetic proteins (BMPs) known to play a role in a variety of skeletal processes. Previous work using the brachypod mouse demonstrated that mice deficient in GDF-5 have long bones with diminished material properties and ash content compared with control littermates. Our aim was to examine the role of a related GDF family member, GDF-7 (BMP-12), in cortical bone by examining the geometric and material contributions to whole bone structural behavior in GDF-7-deficient mice. Femora from 16-week-old GDF-7 −/− animals had significantly smaller bone cross-sectional geometric parameters (e.g., −20% medial/lateral and anterior/posterior moments of inertia). Despite having smaller bone cross-sections, all structural parameters obtained from four-point bending tests were comparable to those of wild-type bones due to elevated cortical bone material properties (+18% modulus of elasticity, +28% yield strength, and +18% ultimate strength). No significant differences in ash content or collagen content were detected, however. These data suggest that GDF-7 deficiency is associated with elevated cortical bone material properties that compensate for decreased geometric properties, thereby preserving bone structural integrity. The compositional and/or microstructural bases for these altered material properties remain to be determined, however.

Ash Content Modulation of Torsionally Derived Effective Material Properties in Cortical Mouse Bone

The purpose of this study was to evaluate the effects of isolated alterations in mineral content on mouse bone torsional properties. The femora and tibiae from 25 eight-week-old male A/J strain mice were divided into five groups and selectively decalcified from 5% to 20%. The right femora were then tested to failure in torsion while the tibiae were ashed to determine final mineral content of the decalcified bones. Contralateral femora were serially cross-sectioned to determine geometric properties, and effective material properties were then calculated from the geometric and structural properties of each femoral pair. We found that the relationship between ash content and effective shear modulus or maximum effective shear stress could best be characterized through a power law, with an exponential factor of 6.79 (R2 = 0.85) and 4.04 (R2 = 0.67), respectively. This indicates that in a murine model, as with other species, small changes in ash content significantly influence effective material properties. Furthermore, it appears that (in adolescent A/J strain mice) effective shear modulus is more heavily affected by changes in mineralization than is maximum effective shear stress when these properties are derived from whole bone torsional tests to failure.

Strength and Regrowth of Hamstring Tendons After Hamstring Autograft Anterior Cruciate Ligament Reconstruction

Summary: Much controversy exists regarding the potential advantages and disadvantages of various graft choices for anterior cruciate ligament reconstruction. Advocates of hamstring autografts often cite the limited apparent morbidity associated with semitendinosus or semitendinosus and gracilis harvest, including evidence that hamstring tendons may regenerate after harvest. In this article, we attempt to summarize the functional, radiographic, and histologic studies to date that examine hamstring regeneration. Ultimately, it appears that tendon-like tissue regenerates in the vast majority of patients, but the anatomic location and biomechanical quality of the neotendon may be inferior. Regardless, functional deficits after hamstring harvest appear to be minimal in most individuals.

Comparison of virtual fluoroscopy to conventional fluoroscopy for C1–C2 transarticular screw fixation

Purpose of study: To compare virtual fluoroscopy to conventional fluoroscopy for transarticular screw fixation in a cadaveric model. Methods used: Twenty-two C1–C2 transarticular screws were placed in 11 cadavers using either virtual fluoroscopy or conventional fluoroscopy. One side of each cadaver was treated using virtual fluoroscopy, and the other side was treated using conventional fluoroscopy; the order of techniques was alternated between consecutive cadavers. Procedure time and fluoroscopy time were recorded. After the procedure, the spines were harvested and analyzed to determine the accuracy of screw placement and length using a standard technique. Measurement of anatomic vertebral parameters was also performed allowing new recommendations for safe screw placement. of findings: Significantly less fluoroscopy time (p=.046) was required in the virtual fluoroscopy group (3.2 vs. 5.7 seconds), although the fluoroscopy time was small in both groups. No significant differences (p<.05) in procedure time were found. In the conventional fluoroscopy group, two screws were found to be partially malpositioned without endangering vital or neurovascular structures. In the virtual fluoroscopy group, there were five malpositioned screws with one screw demonstrating contact with the vertebral artery. Three of the 11 cadavers were found to have unsatisfactory anatomy for C1–C2 screw placement in that the bony corridor for screw placement was small than the diameter of the screw. Relationship between findings and existing knowledge: Virtual fluoroscopy is gaining acceptance in many areas of musculoskeletal surgery. However, there are no reports of the use of virtual fluoroscopy to guide the placement of C1–C2 transarticular screws. Overall significance of findings: Although C1–C2 transarticular screws are known to provide rigid fixation of the atlantoaxial complex, the operative setup and surgical technique remain a challenge. Traditionally, a combination of anatomic and fluoroscopy landmarks are used to guide implant placement. Virtual fluoroscopy has the potential to simplify the setup and procedure, but screw accuracy remains a concern. The results of this study suggest virtual fluoroscopy may lead to decreased accuracy, and therefore further refinement of the technique should be undertaken before it can be recommended for clinical applications. Disclosures: Device or drug: screw. Status: not approved. Conflict of interest: No conflicts.