Computed tomography osteoabsorptiometry-based investigation on subchondral bone plate alterations in sacroiliac joint dysfunction.

Sacroiliac joint dysfunction (SIJD) is an underappreciated source of back pain. Mineralization patterns of the sacroiliac (SIJ) subchondral bone plate (SCB) may reflect long-term adaptations to the loading of the joint. Mineralization densitograms of 27 SIJD patients and 39 controls, were obtained using CT osteoabsorptiometry. Hounsfield unit (HU) values of the SCB mineralization of superior, anterior and inferior regions on the iliac and sacral auricular surfaces were derived and statistically compared between SIJD-affected and control cohorts. Healthy controls showed higher HU values in the iliac; 868 ± 211 (superior), 825 ± 121 (anterior), 509 ± 114 (inferior), than in the sacral side; 541 ± 136 (superior), 618 ± 159 (anterior), 447 ± 91 (inferior), of all regions (p < 0.01). This was similar in SIJD; ilium 908 ± 170 (superior), 799 ± 166 (anterior), 560 ± 135 (inferior), sacrum 518 ± 150 (superior), 667 ± 151 (anterior), 524 ± 94 (inferior). In SIJD, no significant HU differences were found when comparing inferior sacral and iliac regions. Furthermore, HU values in the inferior sacral region were significantly higher when compared to the same region of the healthy controls (524 ± 94 vs. 447 ± 91, p < 0.01). Region mineralization correlated negatively with age (p < 0.01). SIJD-affected joints reflect a high mineralization of the sacral inferior region, suggesting increased SIJD-related mechanical stresses. Age-related SCB demineralization is present in all individuals, regardless of dysfunction.

Systematic Radiation Dose Reduction in Cervical Spine CT of Human Cadaveric Specimens: How Low Can We Go?

BACKGROUND AND PURPOSE: While the use of cervical spine CT in trauma settings has increased, the balance between image quality and dose reduction remains a concern. The purpose of our study was to compare the image quality of CT of the cervical spine of cadaveric specimens at different radiation dose levels. MATERIALS AND METHODS: The cervical spine of 4 human cadavers (mean body mass index; 30.5 ± 5.2 kg/m2; range, 24-36 kg/m2) was examined using different reference tube current-time products (45, 75, 105, 135, 150, 165, 195, 275, 355 mAs) and a tube voltage of 120 kV(peak). Data were reconstructed with filtered back-projection and iterative reconstruction. Qualitative image noise and morphologic characteristics of bony structures were quantified on a Likert scale. Quantitative image noise was measured. Statistics included analysis of variance and the Tukey test. RESULTS: Compared with filtered back-projection, iterative reconstruction provided significantly lower qualitative (mean noise score: iterative reconstruction = 2.10/filtered back-projection = 2.18; P = .003) and quantitative (mean SD of Hounsfield units in air: iterative reconstruction = 30.2/filtered back-projection = 51.8; P < .001) image noise. Image noise increased as the radiation dose decreased. Qualitative image noise at levels C1-4 was rated as either "no noise" or as "acceptable noise." Any shoulder position was at level C5 and caused more artifacts at lower levels. When we analyzed all spinal levels, scores for morphologic characteristics revealed no significant differences between 105 and 355 mAs (P = .555), but they were worse in scans at 75 mAs (P = .025). CONCLUSIONS: Clinically acceptable image quality of cervical spine CTs for evaluation of bony structures of cadaveric specimens with different body habitus can be achieved with a reference mAs of 105 at 120 kVp with iterative reconstruction. Pull-down of shoulders during acquisition could improve image quality but may not be feasible in trauma patients with unknown injuries.

A prospective follow up of age related changes in the subchondral bone density of the talus of healthy Labrador Retrievers.

BACKGROUND: During growth, the skeletal structures adapt to the increased loading conditions and mature to a fully-grown skeleton. Subchondral bone density reflects the effect of long-term joint loading and it is expected to change over time. The aim of this study was to describe the long-term changes in the density distribution of the subchondral bone of the talus of healthy Labrador Retrievers in a prospective study. RESULTS: The subchondral bone density distribution was evaluated using computed tomographic osteoabsorptiometry (CTOAM). Visually, all joints showed very similar density distribution patterns. No significant differences in the topography of the density maxima were found between t1 and t2. The mean density, maximum density, and maximum area ratio (MAR) were significantly increased with increasing age. CONCLUSIONS: The subchondral bone density of the talus of healthy Labrador Retrievers increases with increasing age. It is likely an adaptive response of the subchondral bone due to increased joint loading during growth.

Subchondral bone density distribution of the talus in clinically normal Labrador Retrievers.

BACKGROUND: Bones continually adapt their morphology to their load bearing function. At the level of the subchondral bone, the density distribution is highly correlated with the loading distribution of the joint. Therefore, subchondral bone density distribution can be used to study joint biomechanics non-invasively. In addition physiological and pathological joint loading is an important aspect of orthopaedic disease, and research focusing on joint biomechanics will benefit veterinary orthopaedics. This study was conducted to evaluate density distribution in the subchondral bone of the canine talus, as a parameter reflecting the long-term joint loading in the tarsocrural joint. RESULTS: Two main density maxima were found, one proximally on the medial trochlear ridge and one distally on the lateral trochlear ridge. All joints showed very similar density distribution patterns and no significant differences were found in the localisation of the density maxima between left and right limbs and between dogs. CONCLUSIONS: Based on the density distribution the lateral trochlear ridge is most likely subjected to highest loads within the tarsocrural joint. The joint loading distribution is very similar between dogs of the same breed. In addition, the joint loading distribution supports previous suggestions of the important role of biomechanics in the development of OC lesions in the tarsus. Important benefits of computed tomographic osteoabsorptiometry (CTOAM), i.e. the possibility of in vivo imaging and temporal evaluation, make this technique a valuable addition to the field of veterinary orthopaedic research.

Titanium template for scaphoid reconstruction.

Reconstruction of a non-united scaphoid with a humpback deformity involves resection of the non-union followed by bone grafting and fixation of the fragments. Intraoperative control of the reconstruction is difficult owing to the complex three-dimensional shape of the scaphoid and the other carpal bones overlying the scaphoid on lateral radiographs. We developed a titanium template that fits exactly to the surfaces of the proximal and distal scaphoid poles to define their position relative to each other after resection of the non-union. The templates were designed on three-dimensional computed tomography reconstructions and manufactured using selective laser melting technology. Ten conserved human wrists were used to simulate the reconstruction. The achieved precision measured as the deviation of the surface of the reconstructed scaphoid from its virtual counterpart was good in five cases (maximal difference 1.5 mm), moderate in one case (maximal difference 3 mm) and inadequate in four cases (difference more than 3 mm). The main problems were attributed to the template design and can be avoided by improved pre-operative planning, as shown in a clinical case.

Changes in length of the plantar aponeurosis during the stance phase of gait--an in vivo dynamic fluoroscopic study.

In locomotion, ligaments and muscles have been recognized to support the arch of the foot. However, it remains unclear to what extent the passive and active structures of the lower extremity support the longitudinal arch of the foot during walking. In this study, the mechanical function of the plantar aponeurosis (PA) is investigated by elongation measurements in vivo during the stance phase of gait, in combination with measurements of the mechanical properties of the PA in vitro. Fluoroscopy was used to measure the dynamic changes in PA length and the angular motion of the metatarsophalangeal joint of the first ray, measured during the stance phase (StPh) in 11 feet. Simultaneously, ground forces were measured. Additionally, four cadaver feet delivered topographic information relating to the PA, and three autopsy specimens of PA served to determine the in vitro mechanical properties of PA. The present study revealed a non-significant peak average PA shortening of 0.48% at about 32.5% StPh, followed by a significant average peak elongation of 3.6% at 77.5% StPh. This average peak elongation of 3.6% corresponds to a force of 292N, as estimated by mechanical testing of the autopsy PA specimens. Considering the maximum peak elongation measured in one volunteer of 4.8% at 76% StPh, a peak PA load of 488N might be expected. Hence, with an average body weight of 751N, as allocated to the 11 investigated feet, this maximum peak force would correspond to about 0.65×body weight. As far as we are aware, this is the first report on a dynamic fluoroscopic study of the PA in gait with an appreciable number of feet (11 feet). In conclusion, muscles contribute to support of the longitudinal arch of the foot and can possibly relax the PA during gait. The 'windlass effect' for support of the arch in this context is therefore questionable.

Accuracy of full guided vs. half-guided implant surgery.

OBJECTIVES: The benefit in terms of higher accuracy for full guided implant surgery (template based guided cavity preparation and guided implant insertion) compared with half-guided surgery (template based guided cavity preparation and free-handed, manual implant insertion) has not been proved till now. MATERIAL AND METHODS: A total of 38 identical implants were inserted into five human cadaver jaws, after virtual implant planning with the coDiagnostiX(™) device. All cavities were drilled using templates equipped with tubes for guidance. At random, 19 implants were inserted in a free handed way (half-guided), whereas 19 implants were inserted in a guided way through the templates tubes (full guided). Postoperative cone beam computer tomographies (CBCT) were performed, and based on image fusion the total deviations between the virtual implant positions at the implants base and tip were determined and compared between both implantation modi. RESULTS: The mean difference in accuracy between both implantation modalities at the implants bases was 0.72 mm (range: 0.16-1.17 mm, SD: 0.45). The mean difference in accuracy between both modalities at the implants tips was 0.46 mm (range: 0.16-1.23 mm. SD: 0.49). Although full guided implantation showed a generally higher accuracy (mean tip: 1.54 mm, range: 0.33-3.64 mm; mean base: 1.52 mm, range: 0.4-3.54 mm) than half-guided implantation (mean tip: 1.84 mm, range: 0.84-3.22 mm; mean base: 1.56 mm, range: 0.49-3.43 mm), the differences were not statistically significant. CONCLUSIONS: The accuracy of half-guided implant surgery is comparable with full guided implant surgery.

Computed tomography osteoabsorptiometry is reliable for the determination of the subchondral bone mineralization distribution in the rabbit knee.

Rabbits are among the most frequently used animals in osteoarthritis research. It is meanwhile accepted that the subchondral bone plate (SBP) plays a key role in the development of osteoarthritis. The most suitable technique for analyzing subchondral bone mineralization is computed tomography osteoabsorptiometry (CT-OAM). Because CT-OAM has not yet been applied to smaller animals, the purpose of this study is to test the reliability of CT-OAM in the rabbit knee. Another important task in animal experiments is the intra- and interindividual difference of the measurement parameters. Our hypothesis is that there is no difference regarding both the position of the density maxima and the bone mineral density (BMD) of the SBP comparing right and left tibial plateaus of rabbits. For evaluating the reliability, a rabbit knee was examined by computed tomography 6 times at weekly intervals. The subchondral mineralization distribution was measured by means of CT-OAM. Positions of the density maxima and BMD of the SBP were determined in a standardized procedure. Furthermore, both parameters were evaluated in 6 female White New Zealand rabbits. Positions of density maxima and BMD in the SBP in left tibial plateaus were compared with right tibial plateaus. The relative coefficient of variation as a parameter for reproducibility was 1.6% for determining the position of the density maxima and 1.2% for measuring the BMD. The positions of density maxima and relative BMD between right and left tibial plateaus varied only about 2% intraindividually, whereas interindividual variance was about 10%. In conclusion, determination of the position of density maxima as well as BMD of the SBP by means of CT-OAM is reliable and reproducible in the rabbit knee. We recommend using the contralateral limb as control, because intraindividual accordance of the mineralization patterns and of the BMD of the SBP was higher than interindividual accordance.

Mineralisation and mechanical strength of the subchondral bone plate of the inferior tibial facies.

BACKGROUND: The implantation of total ankle prosthesis is one of the most challenging operations in orthopaedic surgery. The main problem that surgeons face is the fixation of the total ankle prosthesis on the tibial side. The subchondral bone plate of the distal tibia is considered the strongest region on the inferior tibial facies. Based on information about the mineralisation of the subchondral bone plate, conclusions can be made concerning the mechanical stress, age-related changes, post-surgical biomechanical situations and regions of fixation. The aim of this study was to determine the correlation between the mineralisation of the subchondral bone plate and the topical mechanical strength. METHODS: By means of CT-osteoabsorptiometry, the distribution of mineralisation in the subchondral bone plate in 18 distal Tibiae was investigated. After removal of the cartilage of the facies articularis inferior, the mechanical strength of the joint surface was measured with an indentation apparatus. The linear regression of the mineralisation density and the maximal mechanical strength to penetrate the subchondral bone plate was determined. RESULTS: Our data showed a coefficient of determination between 0.75 and 0.97 and a coefficient of correlation between 0.86 and 0.97. The T test showed significance (P < 0.05). Furthermore, we demonstrated a bicentric distribution of mineralisation patterns. The maximal mineralisation was found ventromedially and mediolaterally on the joint surface. CONCLUSION: Our study shows good correlation of mineralisation and mechanical property of the inferior tibial facies. Therefore, as the results provide information on the topographical distribution of bone quality, they could be useful for the development of new fixation methods for total ankle prosthesis.

[Pathologic glenohumeral stress distribution in calcific tendinosis of the supraspinatus]. / Glenohumerale Fehlbeanspruchung bei Tendinosis calcarea der Supraspinatussehne.

AIM: Based on hypothesis that calcific tendonitis of the supraspinatus tendon (CTSSP) could be associated with glenohumeral imbalance, glenohumeral stress distribution was analyzed. METHODS: 26 patient shoulders with CTSSP, unsuccessfully treated by non-operative measures, were examined. A group of 26 macroscopically normal shoulder specimens served as controls. Analysis of glenohumeral stress distribution was indirect evaluating glenoid subchondral bone mineralization by computed tomography osteoabsorptiometry. Density distribution of glenoid subchondral bone mineralization and the position of the two most frequent density maxima were analyzed. RESULTS: Patterns of subchondral mineralization and position of the anterior density maximum were significantly different between both groups. CTSSP mostly presented with a monocentric, anteriorly increased mineralization indicative for a regional increase of stress. The inferior shift of the anterior density maximum demonstrates a parallel shift of glenohumeral stress distribution. CONCLUSION: Mineralization patterns indicate that glenohumeral stress distribution is not physiologic in CTSSP. Moreover, it is comparable with glenohumeral stress distribution as observed in atraumatic antero-inferior glenohumeral instability. Relevance of this observation should be proven for etiology of CTSSP.

A prospective morphological study of facet joint integrity following intervertebral disc replacement with the CHARITE Artificial Disc.

In degenerative disc disease (DDD), increased loading in the posterior column increases facet joint subchondral bone density and may lead to facet joint degeneration. While spinal fusion is commonly used to treat patients with symptomatic DDD, increased stress at the levels adjacent to fusion may accelerate facet joint and adjacent segment degeneration. Artificial disc replacements have been developed as an alternative to fusion. In this prospective study, the effects of disc replacement with the CHARITE Artificial Disc on facet joint loading and integrity were evaluated. Thirteen patients aged <50 years with symptomatic DDD were recruited. Computed tomography (CT) osteoabsorptiometry was performed prior to the implantation of the CHARITE Artificial Disc and six months after. With this technique, increases or decreases in facet joint loading and integrity are indicated by corresponding changes in subchondral bone density. Changes in the distribution of load alter the distribution of the areas of maximum bone density. Clinical outcome was also assessed at pre-operative and 6 and 12 month post-operative visits using the Visual Analogue Scale back and leg pain scores, the Oswestry Disability Index and the Short Form-36 (SF-36) questionnaire. The height of the intervertebral space at the operated level was monitored by lateral X-ray. Subchondral bone density was evaluated in the facet joints of all 13 patients at the operated level, 12 patients at the level above the operated segment, and five patients at the level below the operated segment. Quantitative measurements revealed no significant increases (> or =3%) in subchondral bone density of the facet joints at any level in any patient. Significant decreases (> or =3%) in subchondral bone density were measured at the operated level in 10/13 patients, at the level above the operated segment in 6/12 patients, and at the level below the operated segment in 3/5 patients. There were no changes in the distribution of the areas of maximum bone density in any of the studied facet joints at 6 months compared with pre-operative measurements. Clinical outcome scores were improved at 6 and 12 months compared with baseline. The mean intervertebral space height at the operated level was increased following implantation of the CHARITE Artificial Disc and was 1.8 times greater than the pre-operative height at both 6 and 12 months. In this study, replacement of degenerated intervertebral discs with the CHARITE Artificial Disc was not associated with increased loading of the facet joints at the operated or adjacent levels. Decreases in subchondral bone density may indicate reduced loading in the posterior column following disc replacement compared with loading in the pre-operative degenerated spine. Further study is required to establish the baseline for healthy subchondral bone density and to compare this baseline with long-term measurements in patients undergoing disc replacement.

Quantitative assessment of periarticular osteopenia in patients with early rheumatoid arthritis: a preliminary report.

BACKGROUND: Involvement of the metacarpophalangeal (MP) joints is one of the major problems in patients with rheumatoid arthritis (RA). Although several data about the cumulative influence of steroid intake on bone are available, the course of demineralisation in RA has not been described by quantitative methods until now. PATIENTS AND METHODS: Computed tomography (CT) sections of 96 MP joints in 12 RA patients and of 32 MP joints in four age-matched healthy controls were investigated. Patients were classified according to Steinbrocker. Densitometric evaluation of subchondral bone density was performed by CT osteoabsorptiometry (CT-OAM). Quantitative CT-OAM was used to evaluate mineralisation of the articular surfaces in MP joints. RESULTS: In the distal articular surface of MP joints, the number of density maxima was reduced from 3 to 2.1+/-0.3, 1.9+/-0.5 and 1.3+/-0.3 in RA patients with early, mild to moderate, and severe disease, respectively. Means of calcium concentrations were 633.4+/-35. 3 mg Ca2+/mL, 518.9+/-56.2 mg Ca2+/mL, 497.7+/-23.8 mg Ca2+/mL and 455.1+/-28.6 mg Ca2+/mL for controls and RA patients with early, mild to moderate, and severe RA, respectively. Mineralisation of the distal articular surface was significantly reduced in all groups of RA patients [probability (p) = 0.005]. Regarding the number of density maxima, no differences were detected in the proximal articular surface of normal and RA fingers. However, mineralisation of the proximal articular surface was significantly reduced in all groups of RA patients (p = 0.004). Means of calcium concentrations of the proximal articular surface were 494.1+/-48.5 mg Ca2+/mL, 413.0+/-16.2 mg Ca2+/mL, 406.0+/-51.4 mg Ca2+/mL, 390,4+/-41.1 mg Ca2+/mL for controls and RA patients with early, mild to moderate, and severe RA, respectively. CONCLUSION: Patients with early and untreated RA show loss of mineralisation and altered morphology of the MP joints of the hand, even before corticosteroid therapy. CT-OAM provides evidence for an early alteration of functional anatomy in MP joints.

[Functional CT imaging: Load-dependent visualization of the subchondral mineralization by means of CT osteoabsorptiometry (CT-OAM)]. / Funktionelle Computertomographie: Beanspruchungsabhängige Darstellung der subchondralen Mineralisierung mittels CT gestützter Osteoabsorptiometrie (CTOAM).

PURPOSE: Functional computed tomography for visualization and quantification of subchondral bone mineralization using CT osteoabsorptiometry (CT-OAM). MATERIALS AND METHODS: Tarsometatarsal (TMT) and metatarsophalangeal (MTP) joints of 46 human hallux valgus (HV) specimens were examined (sagittal 1/1/1 mm) on a single slice CT scanner SCT (Somatom Plus 4, Siemens AG). Subchondral bone pixels were segmented and assigned to 10 density value groups (Delta 100 HU, range 200 - 1200 HU) the pixels using volume rendering technique (VRT). The data analysis considered the severity of HV as determined by the radiographically measured HV-angle (a. p. projection). RESULTS: CT-OAM could generate reproducible densitograms of the distribution pattern of the subchondral bone density for all four joint surfaces (TMT and MTP joints). The bone density localization enables the assignment to different groups, showing a characteristic HV-angle-dependent distribution of the maximum bone mineralization of the load-dependent densitogram (p < 0.001). CONCLUSION: CT-OAM is a functional CT technique for visualizing and quantifying the distribution of the subchondral bone density, enabling a noninvasive load-dependent assessment of the joint surfaces. Load-dependent densitograms of hallux valgus specimens show a characteristic correlation with an increase of the HV-angle.

Subchondral mineralization patterns of the glenoid after tear of the supraspinatus.

Clinical experience has shown that in many cases of rupture of the supraspinatus tendon the head of the humerus shifts upward against the acromion. This implicates alterations in the stress acting on the joint surface. Accordingly, this should be reflected by changes in the distribution of the subchondral mineralization on the glenoid. Computed tomography osteoabsorptiometry was used to evaluate the distribution patterns on the subchondral bone plate of the glenoid in 67 human shoulders. The position of the two most frequent density maxima was determined by a standard procedure. In macroscopically normal specimens (n = 24) every case had an anterosuperior density maximum and the majority (75%) also had a posterior positioned maximum. In some instances a third maximum, placed centrally (17%) or in an anteroinferior position (4%) was seen. In shoulders with a torn supraspinatus tendon (n = 43) a third density maximum frequently appeared in the center of the glenoid (42%); however, most notable was a significant change of the posterior maximum position toward central and superior. With increasing size of the tendon defect an extension of the shift of the posterior maximum (superiorly and centrally) was observed in contrast to the constant anterior maximum. The changes in the distribution of glenoid subchondral bone mineralization in shoulders with a supraspinatus tear must be regarded as a morphologic parameter for the altered long-term stress acting on the joint surface.

[Anatomy and biomechanics of the upper ankle joint]. / Anatomie und Biomechanik des oberen Sprunggelenks.

The ankle joint as a component within the construction of the foot must be seen as a compromise between the static and dynamic demands made upon it. In this article the structure and function of the ankle joint are described with special reference to the formation of morphological parameters such as the distribution of subchondral mineralization, cartilage thickness, subarticular cancellous bone and mechanical properties. These parameters could be seen as a biological reflection of the individual mechanical conditions.

[Morphological aspects of load bearing of the wrist joint after midcarpal partial arthrodesis]. / Morphologische Aspekte der Beanspruchung des Handgelenks nach mediokarpaler Teilarthrodese.

Midcarpal fusion is a reliable treatment for advanced carpal collapse following scaphoid nonunion or scapholunate dissociation. It remains, however, unclear if the alignment of the fused carpal bones influences the redirection of load towards the lunate. The objective of this study was to assess the actual loading conditions after midcarpal fusion in patients by evaluating the patterns of subchondral bone mineralization in the distal articular surface of the radius. Nine patients, who were treated by midcarpal fusion with complete excision of the scaphoid, were examined after an average of 22 months postoperatively by means of CT osteoabsorptiometry. All patients showed peak mineralization in the lunate fossa of the distal articular surface of the radius. Six patients with correct carpal alignment had one large density maximum in the lunate fossa and none in the scaphoid fossa. Patients with incomplete correction of the radial translocation of the capitate, incomplete excision of the scaphoid, or incomplete correction of the extension position of the lunate, showed a second density maximum in the scaphoid fossa. These findings emphasize that a correct carpal alignment is necessary to achieve a complete unloading of the degeneratively altered scaphoid fossa.

[Quantitative determination of pressure distribution in the hip joint during the gait cycle]. / Quantitative Bestimmung der Druckverteilung im Hüftgelenk während des Gangzyklus.

The objective of this investigation was the experimental determination of the contact pressures in the hip joint for characteristic phases of the gait cycle. The joint forces determined in vivo with telemetric endoprosthesis by Bergmann et al. (1993) were converted into a pelvic reference system, based on kinematic gait analysis. In eight cadaveric hip joints (age 18-75 yrs.) the reaction forces were applied corresponding to four phases of the gait cycle (heel strike, mid-stance, heel off, toe off) and the pressure distribution determined with FUJI pressure sensitive film. We found maxima of 10 MPa during mid stance. The areas of highest pressure were located in the ventro-superior aspect of the acetabulum (anterior part of the acetabular roof) and in the dorso-inferior aspect of the lunate surface. The pressure distribution was relatively constant during the four phases and the maxima did not vary proportional to the applied load. The normal pressure distribution in the hip appears to be determined by the physiological incongruity of the articular surfaces and the inhomogeneous bony support of the acetabulum. During operative interventions this normal load transfer should be restored as accurately as possible.

Quantitative determination of joint incongruity and pressure distribution during simulated gait and cartilage thickness in the human hip joint.

The objective of this study was to provide quantitative data on hip-joint incongruity and pressure during a simulated walking cycle and on articular-cartilage thickness in the same set of specimens. Using a casting technique in eight specimens of the human hip (age: 18-75 years), we determined the width of the joint space (incongruity) required at minimal load for contact at four phases of the gait cycle. The pressure distribution, measured with pressure-sensitive film, was determined at physiologic load magnitudes on the basis of in vivo measurements of hip-joint forces. Cartilage thickness was assessed with A-mode ultrasound. At minimal loading, the average maximum width of the joint space ranged from 1.1 to 1.5 mm in the acetabular roof, with the contact areas located ventro-superiorly and dorso-inferiorly throughout the gait cycle. At physiological loading, the width decreased and the contact areas covered the complete articular surface during midstance and heel-off but not during heel-strike or toe-off. The pressure distribution was inhomogeneous during all phases, with average maximum pressures of 7.7 +/- 1.95 MPa at midstance. The cartilage thickness varied considerably throughout the joint surfaces; maxima greater than 3 mm were found ventro-superiorly. These data can be used to generate and validate computer models to determine the load-sharing between the interstitial fluid and the solid proteoglycan-collagen matrix of articular cartilage, the latter being relevant for the initiation of mechanically induced cartilage degeneration.

Patterns of subchondral bone mineralization in the wrist after midcarpal fusion.

Midcarpal fusion represents a salvage procedure in cases of advanced carpal collapse, which unloads the scaphoid compartment and redirects the load to the intact lunate compartment of the radiocarpal joint. The aim of this study was to obtain further information about the loading conditions in the living subject by evaluating the pattern of subchondral bone mineralization in patients who have undergone midcarpal fusion of the wrist. Between 4 and 42 months after the surgery, 9 male patients were examined by means of computed tomographic osteoabsorptiometry. All of them showed peak mineralization in the lunate fossa of the radius. Six patients had only one large density maximum in this fossa and no corresponding maximum in the scaphoid fossa. In accordance with our expectations, loading after midcarpal fusion was found to be transmitted mainly through the lunate compartment, a result that was observed even after as little as 4 months, and that thus confirmed subchondral bone mineralization as a valuable parameter for assessment of long-term stress distribution.