Intact Femoral Head Research Articles

Factors related to collapse progression in Japanese Investigation Committee classification type B osteonecrosis of the femoral head.

This study aimed to identify factors related to collapse progression in Japanese Investigation Committee classification type B osteonecrosis of the femoral head (ONFH) and to identify patients who would benefit from surgical treatment. This study included 41 patients (56 hips) with type B ONFH with a minimum follow-up of threeyears. Based on a ≥ 3mm collapse progression in ONFH, we categorised patients into two groups: collapse progression and no collapse progression. Sagittal and coronal computed tomography images were used to measure the necrotic region relative to the intact femoral head diameter. The ratios of the necrotic regions of transverse and vertical diameter in coronal and sagittal images are defined as mediolateral transverse and mediolateral vertical, anteroposterior transverse and anteroposterior vertical, respectively. Demographic data and these imaging findings were compared between the two groups. We established a cut-off value for predicting collapse progression through receiver operating characteristic analysis and determined survival rates. Type B ONFH had a 17.8% collapse progression rate. The mediolateral transverse, mediolateral vertical, anteroposterior transverse, and anteroposterior vertical were significantly higher in the collapse progression group (P < 0.01). Mediolateral transverse was an independent risk factor of collapse progression (hazard ratio, 1.27; 95% confidence interval, 1.03-1.57; P = 0.03), with an optimal cut-off of 45.6%. The 5-year survival rates with collapse progression as the endpoints were 57.0 and 94.9% in the mediolateral transverse of ≥ 45.6 and < 45.6%, respectively. A mediolateral transverse of ≥ 45.6% predicts collapse progression in patients with type B ONFH.

Structural examination of experimental femoral head avascular necrosis

Aim. To conduct histological analysis of femoral head avascular necrosis in Wistar rats.Materials and Methods. Femoral head avascular necrosis was artificially induced in 12 Wistar rats which have been euthanised at 2, 4, 6, and 8 weeks postoperation (n = 3 per time point). Affected and intact femoral heads were examined by X-ray examination, haematoxylin and eosin staining, and scanning electron microscopy.Results. X-ray examination and haematoxylin and eosin staining showed the progressive development of osteonecrosis from 2 to 6 weeks and initiation of bone repair at 8 weeks postoperation. X-ray examination had less informative value as compared to routine histological examination. Progressive loss of bone volume was accompanied by osteolysis, resorption of hyaline cartilage, and replacement of bone and cartilage tissues with collagen fibers. Scanning electron microscopy provided an opportunity to assess cellular composition and showed that the maximum activity of osteoclasts and osteoblasts occurs at 6 and 8 weeks postoperation, respectively.Conclusion. X-ray examination was dispensable when investigating features of femoral head avascular necrosis. Histological examination using haematoxylin and eosin staining permitted detection of bone resorption, while scanning electron microscopy contributed to high-resolution visualisation of the bone cellular composition.

Three-dimensional MRI Analysis of Femoral Head Remodeling After Reduction in Patients With Developmental Dysplasia of the Hip.

Previous reports on patients with developmental dysplasia of the hip (DDH) showed that the prereduced femoral head was notably smaller and more nonspherical than the intact head, with growth failure observed at the proximal posteromedial area. We evaluated the shape of the femoral head cartilage in patients with DDH before and after reduction, with size and sphericity assessed using 3-dimensional (3D) magnetic resonance imaging (MRI). We studied 10 patients with unilateral DDH (all female) who underwent closed reduction. Patients with avascular necrosis of the femoral head on the plain radiograph 1 year after reduction were excluded. 3D MRI was performed before reduction and after reduction, at 2 years of age. 3D-image analysis software was used to reconstruct the multiplanes. After setting the axial, coronal, and sagittal planes in the software (based on the femoral shaft and neck axes), the smallest sphere that included the femoral head cartilage was drawn, the diameter was measured, and the center of the sphere was defined as the femoral head center. We measured the distance between the center and cartilage surface every 30 degrees on the 3 reconstructed planes. Sphericity of the femoral head was calculated using a ratio (the distance divided by each radius) and compared between prereduction and postreduction. The mean patient age was 7±3 and 26±3 months at the first and second MRI, respectively. The mean duration between the reduction and second MRI was 18±3 months. The femoral head diameter was 26.7±1.5 and 26.0±1.6 mm on the diseased and intact sides, respectively (P=0.069). The ratios of the posteromedial area on the axial plane and the proximoposterior area on the sagittal plane after reduction were significantly larger than before reduction (P<0.01). We demonstrated that the size of the reduced femoral head was nearly equal to that of the intact femoral head and that the growth failure area of the head before reduction, in the proximal posteromedial area, was remodeled after reduction. Level IV-case series.

Microarchitecture features and pathology of necrotic region in patients with steroid-induced and alcohol-induced osteonecrosis of femoral head

To investigate the pathological and microstructural features of the osteonecrosis samples from subjects with steroid-induced or alcohol-induced osteonecrosis of the femoral head (ONFH). Thirty femoral head bone samples were collected from ONFH patients who underwent total hip arthroplasty between August 2015 and April 2016. There were 22 males and 8 females. The etiology of ONFH was alcohol-induced in 15 patients and steroid-induced in 15 patients. No significant difference of Association Research Circulation Osseous (ARCO) stage was found between alcohol-induced and steroid-induced ONFH ( Z=2.143, P=0.143). The femoral head bone samples in different areas (necrosis, sclerosis, and normal) from involved subjects was taken, and gross observation, HE staining were carried out (the rate of empty lacunaes was calculated). The intact femoral head was scanned by Micro-CT and the parameters of bone microstructure were analyzed quantitatively. The parameters included bone volume to total volume (BV/TV), bone surface area to bone volume ratio (BS/BV), bone mineral density (BMD), bone mineral content (BMC), structural model index (SMI), trabecular plate number (Tb. N), trabecular plate thickness (Tb. Th), and trabecular spacing (Tb. Sp). As observed in hard tissue slicing of both groups, the integrity of trabecular bone was destructed and cystic lesions left by the bone resorption was replaced by granulation tissues. Significant revascularization was found in granulation tissues of steroid-induced ONFH, but not in the alcohol-induced one. HE staining showed that the bone marrow structure was disordered in both group, as well as bone marrow necrosis and empty bone lacunaes noticed. The structure and integrity of trabecular bone of steroid-induced ONFH was far more severe whereas that of alcohol-induced one were thicker and better. The rate of empty bone lacunae in necrosis area of steroid-induced group was significantly higher than that of alcohol-induced one ( P<0.05), but no significant difference was found in sclerotic and normal areas between 2 groups ( P>0.05). Micro-CT showed that necrotic and sclerotic areas of both groups were low bone density. Bone structure in the former area was mostly heterogeneous. Further blood-rich granulation tissues formation was observed in the same places of hard tissue slicing, while the sclerotic one wasn't. The results of quantitative bone structure analysis showed that BV/TV, BMD, BMC, Tb.N, and Tb.Th of the necrotic and sclerotic areas of steroid-induced ONFH were significantly lower than those of alcohol-induced one ( P<0.01), BS/BV, SMI, and Tb.Sp of steroid-induced ONFH were significantly higher than those of alcohol-induced one ( P<0.01). No significant difference among the indexes above was found in the normal areas of both groups ( P>0.05). The integrity of trabecular bone was destroyed in necrotic area of steroid-induced or alcohol-induced ONFH. However, they performed different features of osteonecrosis and contrasted with each other. The steroid-induced ONFH was characterized by multiple "osteolytic bone destruction", while the alcohol-induced one was manifested by some kinds of "coagulative destruction".

The Central Dislocation of Femoral Head in the Transverse and Both Column Acetabular Fractures: Is It Really Medialized?

PurposeWe hypothesized that the central dislocation of the femoral head does generally not occur in transverse acetabular fractures, although it does usually occur in both column fractures.Materials and MethodsFifty-two transverse and both column acetabular fracture cases were evaluated retrospectively. The distances between (a) the sciatic notch on the fracture side and the vertical axis of the pelvis (VA line) and (b) the contralateral intact sciatic notch and the VA line were measured. The a/b ratio corresponded to the superior iliac segment displacement or rotation. The ratio of the distance between the fracture side femoral head and the VA line (c) and the distance between the contralateral intact femoral head and the VA line (d) corresponded to the femoral head displacement. The width of ischium (e) on fractured side and (f) contralateral side were measured. The e/f ratio increment reflected ischiadic fragment mobility.ResultsThe median value of femoral head displacement (c/d) of the transverse fracture group (n=25) was 1.02 (1.000-1.07). Ischiadic fragment rotation (e/f ratio) of the transverse fracture group was 1.000. The median value of femoral head displacement (c/d) of the both column fractures (n=27) was 0.78 (0.64-0.85). Ischiadic fragment rotation (e/f ratio) of the both-column group was 1.15 (1.06-1.23). The differences between groups according to measurements were statistically significant.ConclusionIn contrary to Letournel description, our findings showed no medialization of femoral head in transverse acetabular fractures in general. This might be an illusion resulting from external rotation of the superior iliac segment.

Surgical Dislocation of the Hip in the Treatment of Complex Osteochondral Injury to the Femoral Head.

The optimal treatment for osteochondral fracture of the femoral head associated with posterior dislocation remains unclear. A case can be made to treat small fragments and those that concentrically reduce nonoperatively. On the other end of the spectrum are those where significant size and residual displacement warrant consideration of operative fixation. This video demonstrates the treatment of a large complex multifragmentary osteochondral femoral head fracture with surgical dislocation. With the patient in lateral decubitus position, the trochanter is approached through lateral incision. The trochanter is cut and capsulotomy performed taking care to preserve the critical medial femoral circumflex artery. Fixation with headless screws is performed from the small comminuted fragments into the dominant section of intact femoral head. Experience suggests that anatomic fixation through surgical dislocation can be carried out with low incidence of subsequent avascular necrosis and degenerative articular change. Given the degree of local osseous and muscular trauma, consideration should be given to prophylaxis of heterotopic bone. Although small osteochondral fragments restricted to the acetabular fossa can be treated nonoperatively, the size and displacement of the presented fragment mandated operative reduction. Given the predicted complexity of repair, the surgical dislocation approach was chosen to provide maximum exposure optimizing the chances for successful fixation.

Study of animal model of osteonecrosis induced by local ethanol injection in emu

To establish a new animal model of osteonecrosis of the femoral head by local ethanol injection in emu. Eight milliliter ethanol was injected slowly to the operated femoral head with customized probe in twenty adult male emus. Postoperatively, hip magnetic resonance imaging was performed at 1, 4, 8, 12 weeks. After emus were sacrificed, the femurs were collected for micro-computed tomography and histological analysis. No emu demonstrated signs of infection or died unexpectedly. Magnetic resonance imaging examination showed broad edema at proximal femur at 1(th) week, and the edema decreased with time, till local edema at femoral head at the 12(th) week. Histological images showed human-like osteonecrotic changes with active bone repair. There were significant differences in trabecular structure and bone mineral density between the operated and intact femoral heads. No collapse was found 6 months after the operation. This emu model of femoral head osteonecrosis by local ethanol injection can progress to early stage osteonecrosis. The different repair methods may have certain correlation with the results of osteonecrosis of the femoral heads.

Traumatic Posterior Hip Dislocation with an Ipsilateral Comminuted Femoral Intertrochanteric Fracture: A Case Report

Traumatic Posterior Hip Dislocation with an Ipsilateral Comminuted Femoral Intertrochanteric Fracture: A Case Report

Resection hip arthroplasty as a feasible surgical procedure for periacetabular tumors of the pelvis

AimsSurgical treatment of periacetabular tumors remains one of the most challenging problems in musculoskeletal oncology. The purpose of this study was to review the clinical and functional outcomes of resection hip arthroplasty and analyze its feasibility. MethodsThis study assesses twenty-seven patients with periacetabular tumors treated by resection hip arthroplasty between 1999 and 2010. The tumors were excised with wide margins and the residual intact femoral head placed underneath the resected ilium. Clinical, functional and oncological outcomes as well as complications were carefully evaluated. ResultsThe average follow-up time was 55 months (range, 3–118) and the mean surgical time 170 min (range, 120–350) with an average blood loss 1200 ml (range, 600–2200). Six patients died in 6–33 months postoperatively; no other local recurrences or deaths occurred. The 1-year, 5-year, and 10-year disease-free survival rates were 96.3%, 77.8% and 77.8% respectively. The mean limb-length discrepancy was 5 cm (range, 2–7.5) and all patients required custom-made shoes with their heels heightened by 2–5 cm. At the last follow-up, the mean functional score was 75.6%. Twenty patients recovered normal ambulation function with custom-made shoes and seven had to walk with crutches. Wound healing problems were observed in nine patients and deep or superficial infection in none. ConclusionsResection hip arthroplasty is recommended as a feasible surgical protocol for periacetabular tumors because it has few complications, good functional results, short surgical time and little blood loss.

Proteomic analysis of the LPS-induced stress response in rat chondrocytes reveals induction of innate immune response components in articular cartilage

Activation of toll-like receptors (TLR) in articular chondrocytes has been reported to increase the catabolic compartment, leading to matrix degradation, while the main consequence of TLR activation in monocytic cells is the expression and secretion of components of the innate immune response, particularly that of inflammatory cytokines. The objective of the work reported here was to obtain a more complete picture of the response repertoire of articular chondrocytes to TLR activation. Mass spectrometry was used to analyse the secretome of stimulated and unstimulated cells. Characterization of TLR expression in rat articular chondrocytes by RT/PCR indicated that TLR4 was the major receptor form. Exposure of these cells to lipopolysaccharide (LPS), the well-characterized TLR4 ligand, induced production not only of the matrix metalloproteinases MMP3 and 13, but also of components traditionally associated with the innate immune response, such as the complement components C1r, C3 and complement factor B, long pentraxin-3 and osteoglycin. Neither TNF-α nor IL-1 was detectable in culture media following exposure to LPS. One of the most prominently-induced proteins was the chitinase-like protein, Chi3L1, linking its expression to the innate immune response repertoire of articular chondrocytes. In intact femoral heads, LPS induced expression of Chi3L1 in chondrocytes close to the articular surface, suggesting that only these cells mount a stress response to LPS. Thus articular chondrocytes have a capacity to respond to TLR activation, which results in the expression of matrix metalloproteases as well as subsets of components of the innate immune response without significant increases in the production of inflammatory cytokines. This could influence the erosive processes leading to cartilage degeneration as well as the repair of damaged matrix.

Editorial: Sub-Capital Hip Fracture: Best Treatment Options

Most orthopaedic surgeons base their decision to treat subcapital fractures of the hip on a set of guidelines. Garden1 in 1971 provided a simple system of grades to guide surgeons. The system is based on displacement of the fracture fragments and relies on the survival of live osteocytes in a compromised, if not totally disrupted, vascular bed. The most displaced fracture—Garden type IV—has no intact nutrient or neck vessels. Only the vessel of the ligamentum teres may survive. Two additional conditions affect the vitality of the displaced femoral head: patient age and the time lapse since fracture. While intra-osseous vessels may not be affected by age, extra-osseous vessels are. Osteocytes do not survive long in the complete absence of a blood supply. Although a few dying osteocytes have been observed within intact femoral head trabeculae for up to 3 weeks after a sub-capital fracture, they appear to be fatally harmed after 12 hours of ischaemia.2 After subcapital fracture, there are no completely reliable techniques to determine whether the femoral head is alive or dead. Even intravital tetracycline labelling and technetium-methylenediphosphonate radionuclide imaging,3 is not completely ‘fool-proof’. Therefore many surgeons do not attempt to treat this fracture by reduction and pinning and opt, from the outset, for an arthroplasty. Preoperative contemplation and planning should bear in mind the acetabular labrum and the posterior capsule. If a monopolar replacement is chosen, the capsule of the hip should be carefully preserved and, in particular, the acetabular labrum. The labrum increases the dimensions of the acetabular space and reduces the likelihood of postoperative dislocation. In patients who are likely to be sitting in bed or in a wheelchair, an anterior approach will reduce the risk of hip dislocation. The converse is true following a posterior approach. The patient’s level of activity must also be considered. It influences the choice of arthroplasty. Few people at high risk for subcapital hip fracture are tennis players, but if an individual is very active, a total hip arthroplasty (THA) is better able to withstand hard work and heavy-duty sports, such as skiing, than other treatment options.4 Blood transfusion increases the risk of wound infection and should be avoided if at all possible. Among patients who have had surgery for intracapsular fractures of the hip, the overall risk of wound infection is about 4.5%. It is about 7.0% in those who are transfused in contrast with only 3.71% in the non-transfused.5 Hence a ‘less-blood-losing’ operation would seem particularly advantageous in this type of surgery, although it is best to avoid blood transfusions in any type of surgery. The above-listed caveats influence the decision on the best choice of femoral head replacement.

Proton MR spectroscopy of the femoral head—Evaluation of patients at risk for avascular necrosis

To detect alteration of the fatty component by measuring the in vivo lipid and water content of normal-looking femoral heads of patients with and without risk for avascular necrosis (AVN) by using proton MR spectroscopy (MRS). Marrow composition was measured by proton MRS (TR/TE = 5000/20 msec) in a sample volume placed in the epiphysis of the intact femoral heads of patients with unilateral osteonecrosis of the hip (group 1, N = 61, then excluding the post-traumatic or steroid user, final N = 45) and age-matched controls (group 2, N = 49). Three response variables were derived from MRS: the lipid linewidth (LW), water LW, and lipid/water ratio. Of the three variables, the lipid and water LWs differed significantly between groups (P < 0.001 and P = 0.05, respectively; t-test). The lipid/water ratio had borderline significance (P = 0.06). The three variables differed significantly between groups when multivariate regression (P < 0.0001) was analyzed; and age and sex had no significant effect on the three dependent variables. Proton MRS can depict alteration in the lipid and water composition of normal-looking femoral heads with and without AVN on the contralateral hip. Proton MRS may be a potential tool for investigating of the femoral head component in vivo and predicting the risk for development of AVN.

Processing of Whole Femoral Head Allografts: Validation Methodology for the Reliable Removal of Nucleated Cells, Lipid and Soluble Proteins Using a Multi-step Washing Procedure

Following the major outbreak of BSE in the United Kingdom in the mid 1980's and the first reported cases of the human disease equivalent, vCJD, in 1996 a number of measures were taken to reduce the risk of secondary transmission of vCJD by blood or surgical instruments. Two cases of probable transmission of vCJD by blood components have now been reported. The Department of Health has recently undertaken a vCJD risk analysis for bone. Although significant uncertainties still exist in the assumptions on which the assessment is based, a few important recommendations were made. These include a recommendation that bone should be processed to remove blood and marrow and that pooling of donations is never advantageous. This study aimed to establish a method of processing whole femoral heads using disposable equipment, with the purpose of removing as much of the marrow components as possible. We are able to remove 98.2% (range 94.5-99.9%) of the nucleated cells and 98.7% (range 97.8-99.4%) of the soluble protein content from within an intact femoral head. This work confirms that the majority of blood and marrow components can be removed without the need for morselising the bone prior to washing.

The effect of freezing and intraosseous fluid on the stiffness behavior of canine trabecular bone.

The effect of disrupting the intraosseous fluid compartment and freezing on the mechanical stiffness of trabecular bone in intact canine femoral head specimens was investigated. Twenty-four skeletally mature dogs were divided into two groups. Twelve paired fresh femora were tested and 12 paired femora were tested after freezing at -20 degrees C. The intact femoral head specimens were subjected to a load of physiologic magnitude, and then the stiffness of the underlying trabecular bone was determined in intact femora, in drilled femora with a disrupted intraosseous fluid compartment, and subsequently after refilling the compartment with fluid. Drilling of the femoral head and disrupting its bony fluid compartment resulted in a 40% decrease in stiffness (P<.001). This effect was seen only with fresh specimens and not frozen specimens. Refilling the bony compartment with fluid restored the stiffness of the fresh femoral head. These results demonstrate the mechanical properties of trabecular bone in canine femoral head specimens in vitro are affected by intraosseous fluid and freezing. Removal of the intraosseous fluid decreases the mechanical stiffness of canine trabecular bone, and freezing the specimens appears to alter the intraosseous fluid compartment behavior. It is necessary to gain a better understanding of the dynamic mechanical properties of intact bone to improve the existing analytical and experimental mechanical bone models. The effect of intraosseous fluid and freezing should be considered in these models.

Prognostic precision in postoperative 99mTc-MDP scintimetry after femoral neck fracture.

A 2-year follow-up regarding healing complications, such as redisplacement, nonunion, and segmental collapse of the femoral head, was performed in 306 patients operated on for femoral neck fracture and examined with 99mTechnetium-MDP scintimetry within 2 weeks postoperatively. Scintimetric evaluation was performed by selecting regions of interest over the femoral head on the fracture side and the intact side and by comparing the uptake. A femoral head ratio fractured/intact side thus was obtained. Of 199 patients with an intact femoral head uptake (ratio greater than or equal to 1.0), 181 showed no signs of healing complications at 2 years, whereas 18 had developed healing complications. Of 107 cases with a deficient femoral-head uptake (ratio less than 1.0), 96 had developed healing complications within 2 years from the operation, while 11 cases had no signs of radiographic complications. We conclude that 99mTc-MDP scintimetry performed within 2 weeks from femoral neck fracture can predict the outcome of the healing course with a prognostic accuracy of 91 per cent.

Susceptibility of cartilage to damage by immunological inflammation.

Injection of ovalbumin into subcutaneous air pouches prepared on the backs of rats previously sensitised to the antigen resulted in the induction of a small and transient accumulation of inflammatory fluid with a predominantly polymorph cell infiltrate. Challenge of pouches of appropriately sensitised rats with Bordetella pertussis vaccine, on the other hand, resulted in a larger and more prolonged accumulation of fluid and cells with a predominantly mononuclear presence. When intact homologous femoral head cartilage was implanted in these inflamed pouches proteoglycan loss was found to be not different from similar implants in non-inflamed pouches. Coating the cartilage with human heat-aggregated immunoglobulin G prior to implantation in air pouches was also found to be without effect on subsequent proteoglycan loss.

Technetium-99m-methylenediphosphonate Scintimetry after Femoral Neck Fracture A Three-year Follow-up Study

Thirty-nine patients with femoral neck fractures were followed up clinically and radiographically by technetium-99m-methylenediphosphonate (99mTc-MDP) scintimetry two to 20 days and four, eight, 12, 24, and 36 months after surgery or until redisplacement, pseudarthrosis, or segmental collapse occurred. The scintimetric data were calculated by selecting regions of interest on the fractured and intact sides over the femoral head, neck, greater trochanter, and shaft; ratios of fractured/intact side were obtained for each region. Bone metabolism after femoral neck fracture was expressed and analyzed numerically. Prognosis regarding the course of healing could be made with precision by studying femoral head isotope activity shortly after surgery, preferably one to three weeks after operation. Intact femoral head uptake (ratio greater than 1.0) was connected with uneventful healing, while defective uptake (ratio less than 1.0) was observed with healing complications. The vast majority of femoral heads with primary uptake defects showed increased uptake (greater than 1.0) after four months, often as early as six to eight weeks, indicating revascularization. Segmental collapse, as well as redisplacement and pseudarthrosis, appear to be related to femoral head vascular injury. Femoral head uptake in patients in whom healing complications developed secondary to avascularity differed significantly from that in patients with normal healing, except at investigations performed four to eight months after operation. 99mTc-MDP uptake in the femoral neck, trochanter, and shaft areas was increased for all femoral neck fractures. Subsequent normalization was considerably slower in patients with healing complications. A significant difference from normal healing did not occur until 12-24 months after operation. For patients with contralateral hip disease affecting the femoral head ratio, the prognosis regarding complications was made with the aid of the femoral head/shaft ratio on the fracture side.

Femoral head vitality after femoral neck fracture. Comparison between pre- and peroperative tetracycline labeling.

Using fluorescence microscopy, a ratio between tetracycline labeling of the femoral head and of the greater trochanter was calculated for 370 femoral neck fractures. Sixty-three patients were given tetracycline on admission to hospital and 307 on the operating table after closed reduction. The following results were obtained: Visual grading of labeling correlated well to a distribution analysis based on a morphometric point-wave pattern. No significant difference concerning the degree of labeling between the pre- and peroperative groups was found. A redistribution into groups according to fracture displacement (Garden I-IV) did not alter this fact. In the total material, labeling was significantly better for undisplaced than for displaced fractures. No difference was found between different degrees of displacement. For patients less than 50 years of age, labeling values were significantly lower. Intact femoral head vascularization (ratio greater than or equal to 0.90) was found in less than three per cent of the total material.

Variation of chemical composition with age in human femoral head cartilage.

The chemical composition of intact femoral head cartilage was investigated with age. Full-depth cartilage showed a decrease in water content and an increase in keratan sulphate and noncollagenous material with age. When analyzed through the depth of the cartilage, keratan sulphate was shown to appear first in the deep zones and later in the surface, while water content was lost mainly in the deep zones. On a dry weight basis collagen content decreased with age. This was not a real loss but was due to a change in the proportions of other materials, mainly in the deep zones.

Fatigue fracture in the subchondral bone of the human cadaver femoral head.

(1) The strains occurring in the subchondral bone of the cadaver human femoral head were measured when the head was subjected to a load of physiological magnitude and direction. (2) The strains were tensile around the circumference of the femoral head and compressive in the plane of the applied load. (3) In the intact femoral head the magnitude of the strains was such that fatigue fracture of the subchondral bone would not be expected to occur in life. (4) When a cylindrical defect 13 mm in length and 10 mm in diameter was made in the centre of the femoral head, the measured strains in the subchondral bone invariably rose, and in some femoral heads the calculated stresses were high enough to be likely to cause fatigue fracture. (5) It is concluded that cysts developing in the femoral head in osteoarthrosis may usually result in a rise in the stresses in the subchondral bone, with a possible consequent revascularization of the overlying cartilage either via a fatigue crack or by reason of the vascular changes accompanying the healing of an incipient fatigue crack. The probability of either of these events cannot be assessed accurately with the information available, but it appears to be low.