Reversibility of nontraumatic disuse osteoporosis during its active phase.

The potential for the recovery of bone lost during the active phase of disuse osteoporosis, both in the diaphyseal compacta and metaphyseal spongiosa was tested in young adult and old Beagle dogs. Immobilization for up to 60 weeks was achieved by placing the forelimb in a spica cast and remobilization by removing it. Bone volume was estimated in the third metacarpus, radius, ulna and humerus at the mid-diaphysis and at the level of distal metaphyseal spongiosa in both forelimbs by radiography and histomorphometry. Measurements carried out on animals remobilized showed considerable recovery of the original bone loss. In both age groups, the residual deficits increased, however, with the duration of immobilization and were similar in the metaphyseal spongiosa and in the diaphyseal compacta. The old dogs which began the study with 10% less bone than the younger dogs, showed smaller proportional losses than the younger dogs but greater residual deficits, most evident in the diaphysis. In both age groups the distal, weight-bearing bones tended to show greater losses and also greater recovery both in diaphyseal compacta and the metaphyseal spongiosa. Thus, 28 weeks after cast removal following 32 weeks of immobilization the following findings were noted: In the third metacarpal diaphyseal compacta in the younger dogs, a 53.6% loss (mostly from the periosteal envelope) decreased to 16.3% (a 70% recovery) while in the older dogs a 37.6% loss (mostly from the endosteal envelope) decreased to 23% (a 40% recovery).(ABSTRACT TRUNCATED AT 250 WORDS)

Pattern of bone loss of the proximal femur: a radiologic, densitometric, and histomorphometric study.

The pattern of bone loss in the proximal femur was studied in 141 cadaveric femora from 36 women and 39 men ranging from 27 to 89 years of age. Bone mineral density (BMD) of the femoral neck, greater trochanter, Ward's triangle, and tensile and compressive stress regions were measured by dual photon absorptiometry. Radiographs were graded by Singh's method. Histomorphometry of tensile and compressive trabecular areas was performed on ground midsection of the methylmethacrylate-embedded whole proximal femur. Although Singh index had some correlation with BMD of the femoral neck, the various BMD measurements showed that all regions lost bone to the same extent; in particular, no selective bone loss was found at low stress regions (tensile trabeculae or Ward's triangle). Histomorphometry revealed that most of the trabecular bone loss of the proximal femur is attributable to a decrease in thickness of individual trabeculae.

Influence of stable fixation on trabecular bone healing: a morphologic assessment in dogs.

The healing patterns of trabecular bone are different from those of compact bone. In order to investigate further this observation, a histomorphometric assessment was undertaken. The influence of internal fixation devices on trabecular bone healing was also studied. Intercondylar osteotomies were produced in 19 dogs and fixed with screws. All dogs were killed between 1 and 14 weeks; eight of them had the screws removed 4 weeks after osteotomy and were killed 4 or 10 weeks later. The results of morphometry were compared to the histologic and radiologic pictures. Anatomic reduction with stable fixation led to contact healing characterized by a narrow endosteal bone formation at the osteotomy site that disappeared only after union was complete (4 weeks). In gap healing, the endosteal bone formation was greater. Internal fixation devices appeared to cause a diffuse osteopenia once union was complete. Their removal just after completion of union seems to prevent the bone loss. Screws induced bone formation around their threads; after they were removed, the reaction disappeared but the screw holes were not filled with normal trabeculae 10 weeks later. Union of fractures through trabecular bone can be assessed radiologically. A decrease of band-like bone density at the fracture site indicates completion of union. This is the optimal time for implant removal. It prevents the osteopenia observed in cases of continuous presence of screws.

Growth in width of the metacarpals--an investigation in human fetuses.

The process of growth in width of the human hand during fetal life has never been described. Do metacarpals grow concentrically and separation between the bones occurs through expansion of soft tissues? Or is growth eccentric, a process termed drift by Enlow, a relocation in space of organs? Hands of 10 spontaneously aborted fetuses (age range: between 14.5 and 24 weeks of gestation) were examined paying special attention to the bone bark. A thicker bone bark was taken as an indication of growth in that direction. The thickness of the bone bark was measured at the radial and ulnar sides at the level of the proximal and of the distal physes of the second to fifth metacarpals. A ratio of radial over ulnar bone bark thickness (R/U ratio) was calculated. The third metacarpal grew almost concentrically (R/U ratio 1.12 +/- 0.06). The second metacarpal grew in a radial direction (R/U ratio 3.29 +/- 0.19) and the fourth and more so the fifth metacarpal grew in an ulnar direction (R/U ratio 0.70 +/- 0.04 and 0.42 +/- 0.02, respectively). The differences in R/U ratios between every metacarpal were statistically significant for all comparisons P < or = 0.001. Fetal growth in width of the human metacarpals is eccentric and not concentric. It is concluded that during growth in width the metacarpals move away from the midline of the hand and that growth occurs through eccentric bone apposition rather than through soft tissue expansion.

Two processes of bone remodeling in plated intact femora: an experimental study in dogs.

Bone loss is known to occur under plates used for internal fixation. Its exact location and extent and its relationship to the plate-bone contact area was investigated in 36 adult beagles. Plates with two different contact areas were fixed unilaterally to intact femora for periods of 8 and 24 weeks. After removal, the bones were assessed radiographically, histologically, histomorphometrically, and biomechanically. Two processes that affect the bone after plating became apparent. One is a short-term process, possibly caused by the interference of the plate with the blood supply to the cortex. This is followed by necrosis, which induces porosis. The second independent process is caused by the tendency of the bone to adapt to the new state of mechanical loads that results from the load sharing by the plate. The first stage of this process is expressed through swift changes in the bone cross-sectional area under the plate by remodeling in all three envelopes: haversian, periosteal, and endosteal. This stage is followed by a gradual remodeling towards a steady state, in which the final cross-section of the bone is attained. Both processes affected the bone simultaneously during plate fixation. The process caused by the vascular interference ceases after some time, and only the process due to stress-shielding prevails for a long period.

Degeneration at the insertion weakens the tensile strength of the supraspinatus tendon: a comparative mechanical and histologic study of the bone-tendon complex.

The purpose of this investigation was to determine the relationship between the degree of degeneration at the supraspinatus insertion, the tensile strength, and the site of failure of this tendon. Thirty-three fresh cadaveric shoulders (average age: 62 years; range: 39-83 years) were examined. A tensile load to failure was applied at a constant crosshead speed of 25.4 mm/min to a 10 mm wide strip of the supraspinatus tendon that remained attached to the bone. Preexisting degenerative changes at the insertion were assessed and scored histologically and compared with the ultimate tensile stress. Twenty tendons failed at the insertion (the insertion group), and 11 failed in the midsubstance (the midsubstance group). The histologic score of degeneration for the insertion group was significantly higher than that for the midsubstance group (p = 0.0026). There was a negative correlation between the ultimate tensile stress at the insertion and the degeneration score for the insertion group (r = -0.60; p = 0.013). Histologic observations revealed that disruptions of tendon fibers were located mostly in the articular half of the tendon and that they enlarged during mechanical testing in 90% of the specimens of the insertion group. It seems that degenerative changes at the supraspinatus insertion reduce the tensile strength of the tendon and constitute a primary pathogenetic factor of rotator cuff tear.

Cortical porosis under plates. Reaction to unloading or to necrosis?

Cortical porosis under plates used for the fixation of fractures is often attributed to the interference of the plates with cortical perfusion, resulting in necrosis, which in turn induces remodeling. To our knowledge, no histomorphometric studies have been published that demonstrate the correlation between cortical necrosis and porosis. The objective of this study was to test the hypothesis that cortical necrosis is related to changes associated with porosis. Standard and railed plates were applied to intact femora in ten dogs. Histomorphometric studies done at eight and twenty-four weeks after insertion of the plate failed to show a significant positive correlation between necrosis and porosis irrespective of the type of plate used. Porosis was always greater in the inner cortical sector, where no increased necrosis was noted, than in the outer cortical sector, where necrosis was present.

Histomorphic analysis of the development of the pars interarticularis and its association with isthmic spondylolysis.

STUDY DESIGN: Descriptive study analyzing the histologic development of human fetal lumbar spine pars interarticularis. OBJECTIVES: To delineate the histologic development of the fetal pars interarticularis and correlate the development of the pars with isthmic spondylolysis. SUMMARY OF BACKGROUND DATA: Isthmic spondylolysis is present in 5% to 6% of the population. The incidence at birth is zero but rises sharply to 5% at age 4 to 5 years. The origin of the lesion is unknown; however, the current theory states that isthmic spondylolysis results from a fatigue fracture through a congenitally weak pars interarticularis. No study exists investigating the histologic development of the pars. METHODS: Microscopic examination of lumbar spines of human fetuses aged 8-20 weeks' gestation was performed. Specimens were dissected en bloc, decalcified, embedded in paraffin wax, sectioned and fixed on glass slides, and stained. RESULTS: The pars begins to ossify at 12 to 13 weeks' gestation by endochondral ossification. The ossification center originates in the region of the pars in lower lumbar vertebrae, resulting in uneven distribution of trabeculation and cortication in this region. The ossification center arises at the end of the pedicle in upper lumbar segments giving rise to uniform trabeculation through the pars. CONCLUSIONS: Uneven distribution of isthmic ossification results in formation of a potential stress riser in the region of the pars in lower lumbar vertebrae, which could be susceptible to fatigue fracture.

Ultrastructural localization of calcium in calcifying tendinitis.

To determine the site of mineralization in calcifying tendinitis, we studied the ultrastructure of tendon fragments that were obtained during surgical interventions on ten patients with that condition. We found that calcification was occurring extracellularly and essentially in areas where the tendon had undergone cartilaginous transformation. Calcific crystals were present in matrix-vesicle-like structures that were seen either singly among collagen fibers or in aggregates. When they were in aggregates, the calcifying vesicles tended to fuse with each other. Thus, the process of mineralization in calcifying tendinitis resembled those calcifying conditions that have already been described in man and animals, both normal and pathological, in which the apatite crystals are initially localized in matrix vesicles.

Prenatal development of the iliolumbar ligament.

Serial sections, in the frontal plane, of 12 human fetuses showed that the iliolumbar ligament was always present at the gestational age of 11 to 15 weeks; in younger specimens, it could not be identified. The ligament develops during the prenatal period and is not formed by metaplasia of the quadratus lumborum muscle during the second decade of life.

The effects of metal plates on post-traumatic remodelling and bone mass.

The long-term effect of stainless steel and titanium alloy plates on structural remodelling and bone mass of osteotomised canine femora was studied and the effects of early and late removal of plates were compared in 27 adult Beagles. Radiological, histological, histomorphometric and tetracycline fluorescence studies led to three conclusions. First, the continuous (60 weeks) presence of plates, irrespective of their composition, delays remodelling and leads to a reduction of bone mass. This loss is significantly greater under stainless steel plates. Secondly, the removal of plates at eight weeks leads during the 52 ensuing weeks to a marked and widespread structural remodelling and to a return to normal bone mass, irrespective of the type of plate used. However, remodelling is more intense after titanium alloy plates have been used; it is not complete 60 weeks after osteotomy. Thirdly, removal of plates at 40 weeks activates remodelling during the ensuing 20 weeks to a lesser degree and to a more limited extent than early plate removal. The clinical significance of this study is that less rigid but stable internal fixation permits the radiological assessment of healing and thus the determination of the optimal moment for removal of the plates. It also reduces the degree of bone loss should the plate be left in situ for any reason.

Surgical repair of rotator cuff ruptures. The importance of the subacromial bursa.

We examined biopsy specimens obtained during surgery on 115 patients with complete rotator cuff rupture. The vascularised connective tissue covering the area of rupture and the proliferating cells in the fragmented tendons reflected more of the features of repair than of degeneration and necrosis. The main source of this fibrovascular tissue was the wall of the subacromial bursa. These features clearly indicated a vigorous reparative response which might play an important role in tendon reconstitution and remodelling. We therefore suggest that extensive debridement along with subtotal bursectomy, commonly practised during surgical repair of rotator cuff rupture, should be avoided. Although strong suture margins are essential for good operative results, debridement should be judicious and preserve as much as possible of the bursa and the associated fibrovascular tissue.

Bone loss in response to long-term immobilisation.

The histodynamic response to long-term "non-traumatic" immobilisation was studied in young adult Beagle dogs by means of radiomorphometry and histomorphometry, the right forelimb being encased in plaster and the left forelimb serving as a control. The dogs were killed at two, four, six, eight, twelve, sixteen, twenty, twenty-four, thirty-two and forty weeks and the third metacarpal, radius, ulna and humerus removed for analysis of the contributions of the periosteal, haversian and endosteal envelopes to the bone loss at the mid-diaphysis. The bone mass responded to long-term immobilisation in three stages. First there was a rapid initial loss of bone, reaching its maximum (some 16 per cent of original mass) at six weeks, to which all three bone envelopes, to some extent, contributed. A rapid reversal followed, the bone mass approaching the control values between eight and twelve weeks after immobilisation. A second stage of slower but longer lasting bone loss ended twenty-four to thirty-two weeks after immobilisation; the periosteal envelope was the main contributor (80 to 90 per cent of the total loss). The third stage was characterised by maintenance of the bone mass which had been reduced by some 30 to 50 per cent of original values. This pattern was qualitatively similar in all four bones but the distal bones lost more bone than the proximal bones. The extent of resorption surface and the total histologically "active" periosteal envelope increased parallel to the phases of bone loss. The linear mineralisation rate did not differ significantly between the experimental and control sides.

Anterior capsular redundancy of the shoulder: congenital or traumatic? An embryological study.

A study of the attachment of the joint capsule to the scapula, and of the shape of the humeral head, has been carried out in 52 fetal and embryonic shoulders. In 77% of cases the anterior capsule was attached to the labrum or close to it; in the remaining 23% it was inserted into the neck of the scapula, so creating a pouch. In all 52 specimens the humeral head was spherical. It was concluded that the pouched and redundant anterior capsule sometimes seen during surgery for recurrent dislocation of the shoulder, may not be traumatic in origin, but could be a developmental variant.

The pathogenesis of club foot. A histomorphometric and immunohistochemical study of fetuses.

We studied 16 club feet and 27 normal feet from spontaneously aborted human fetuses in the second trimester of gestation and measured the length of the spring ligament, and the declination angle and size of the talus. We also studied the cellular characteristics of the spring ligament and the immunohistochemical features of the medial ankle ligaments using monoclonal antibodies against type-III collagen, desmin, vimentin, and smooth muscle actin. Histomorphometric results indicated that the talar deformity was not the primary lesion. Histological and immunohistochemical findings showed that the cells and collagen fibres of the medial ankle ligaments of club feet appeared to be the site of the earliest changes, in that they had lost their spatial orientation and had contracted. In severe club feet before the third trimester of gestation, myofibroblast-like cells seemed to create a disorder of the ligaments resembling fibromatosis. This led to contraction and resulted in typical club-foot deformity.

Anteversion of the acetabular cup. Measurement of angle after total hip replacement.

We describe a new method for the accurate measurement of the angle of anteversion of an acetabular cup from standard anteroposterior radiographs, and provide the conversion tables required. The effect of the centering of the radiograph is discussed and a method of distinguishing between anteversion and retroversion by using a caudally directed x-ray beam is described.

Early reactions after reimplantation of the tendon of supraspinatus into bone. A study in rabbits.

In 14 rabbits we determined the origin of the cells effecting healing of the tendon of supraspinatus inserted into a bony trough. After two weeks both the cellularity of the underlying bone and the thickness of the subacromial bursa were significantly increased in the operated compared with the control shoulders. The cellularity of the stump of the tendon, however, was significantly decreased in the operated shoulders. In this model, both the underlying bone and the subacromial bursa but not the stump of the tendon contributed to the process of repair. We conclude that the medial stump should be debrided judiciously but that cutting back to bleeding tissue is not necessary during repair of the rotator cuff. Moreover, great care should be taken to preserve the subacromial bursa since it seems to play an important role in the healing process.

The advantages of titanium alloy over stainless steel plates for the internal fixation of fractures. An experimental study in dogs.

An experimental study is reported of fracture healing in the femora of 36 Beagle dogs, comparing the results of using stainless steel plates with those of using less rigid titanium alloy plates. The alloy plates led to the appearance of a small amount of periosteal callus without any histological evidence of fracture instability, thus allowing the radiological assessment of fracture union. This also produced less bone loss during the remodelling phase. Radiological measurements 24 weeks after osteotomy showed cortical thickness to be reduced by six per cent under titanium alloy and by 19 per cent under stainless steel, while histological measurements showed a total bone loss of 3.7 per cent under titanium alloy and of 11 per cent under stainless steel plates. Removal of the titanium alloy plates after eight weeks followed by a recovery period of 16 weeks produced an increase of cortical thickness of 69 per cent and a gain in total bone mass of 30 per cent. Titanium alloy plates also produced less soft-tissue reaction than stainless steel plates. It is concluded that this alloy is a promising material for internal fixation devices.

Pathogenesis of soft-tissue contracture in club foot.

We investigated the pathogenesis of soft-tissue contracture in club foot, using immunohistochemistry to study 41 biopsy specimens and 12 normal deltoid ligaments from cadavers. Five biopsy specimens were studied by electron microscopy (EM) to determine the presence of myofibroblasts. All 41 specimens of club foot stained positively for vimentin as against only one of the 12 control specimens. By contrast, there was no difference in staining for desmin or alpha-smooth muscle actin. EM showed some variability in the appearance of ligamentous cells. Most contained bundles of microfilaments in the cytoplasm and many had abundant pinocytotic vesicles, but no basal lamina or plasmalemmal attachment plaques. Cells of the medial ligamentous tissue in patients with club foot contain vimentin and others have myofibroblastic characteristics. Both features may contribute to recurrence after soft-tissue release.

Structural disorders at the insertion of the supraspinatus tendon. Relation to tensile strength.

We examined macroscopically and microscopically 55 cadaver rotator-cuff tendons attached to their humeral heads to determine the distance between the edge of the articular cartilage and the tendon insertion of the supraspinatus (the width of the sulcus) and the score of regressive changes at the sulcus. In 33 specimens we measured the tensile strength. The width of the sulcus was correlated with the score of regressive changes and with the ultimate tensile strength of the supraspinatus tendon. The width of the sulcus correlated positively with the score of regressive changes (r = 0.66, p < 0.0001), but there was a negative correlation between the latter and the ultimate tensile strength (r = -0.81, p = 0.001) and between the width of the sulcus and the ultimate tensile strength (r = -0.74, p = 0.004). We believe that the width of the sulcus is a simple and useful clinical indicator of the integrity and the tensile strength of the supraspinatus tendon.