Influence of cartilage geometry on the pressure distribution in the human hip joint.

To elucidate the role of mechanical factors in the etiology of osteoarthritis, the detailed geometry of the weight-bearing cartilage layer over the human hip socket is compared with the corresponding pressure distribution. The shape of the pressure distribution is strongly correlated with the shape of the cartilage compression distribution.

A protein expressed in the growth cones of embryonic vertebrate neurons defines a new class of intermediate filament protein.

We have isolated and characterized cDNAs that encode a protein expressed in the axons and growth cones of a subset of Xenopus embryonic neurons. The protein is also expressed in a subset of cells of the brain, including cells in even-numbered rhombomeres, the eye, and the heart. The sequence of the cDNA suggests that the protein belongs to a new class of neural-specific intermediate filaments. Both the RNA and the protein are expressed in the neurula and persist during embryogenesis in the brain, cranial nerves, and spinal cord. Because of the predicted structure of the protein, we have named it tanabin (from the Persian word for rope).

In vivo hip pressures during cane and load-carrying gait.

OBJECTIVE: To test the hypotheses that carrying a load reduces hip contact pressure ipsilateral to the load and that using a cane when carrying a load further reduces hip contact pressure. METHODS: A Moore-type endoprosthesis with 13 femoral-head pressure transducers was implanted in a human subject following a Garden III fracture. Hip contact pressures were measured during unaided, cane-aided, and load-carrying gait over two years. RESULTS: Relative to unloaded gait, contact pressures increased significantly when ipsilateral to the carried load. Using a contralateral cane when carrying the load reduced ipsilateral posterior-superior contact pressure; however, the hip contralateral to the load experienced significantly higher than normal pressures. CONCLUSIONS: Ipsilaterally carried loads may not always provide stress protection of the arthritic hip. Using a cane opposite to the load may aid in restoring normal pressures to the ipsilateral hip, but may expose the contralateral hip to a significant stress burden.

Experimental temperature rise in human hip joint in vitro in simulated walking.

Although reported frictional coefficients in synovial joints are very low, a computer model of the human hip joint in simulated walking predicted a temperature rise of several degrees Celsius. To confirm this prediction, physical experiments were conducted in vitro on intact human hip joints dynamically loaded and articulated as in walking. Thermisters were placed in subchondral bone in both the acetabulum and femoral head, just below the cartilage layers. The surrounding saline bath was maintained at 37 degrees C. Measured temperatures as high as 2.5 degrees C above the 37 degrees C were recorded in the subchondral bone. Loading that simulated the stance/swing phases of gait but without articulation produced no significant increase in temperature; thus fluid flow per se is not significantly energy dissipative; the prime source is friction at the articulating surfaces.

Induction of heat-shock protein synthesis in chondrocytes at physiological temperatures.

Induction of heat-shock protein (HSP) synthesis is demonstrated in cultured calf-chondrocytes at temperatures shown to occur in normal human cartilage during experiments subjecting intact cadaverous hip joints to the parameters of level walking. A 70,000 MW heat-shock protein (HSP-70) is synthesized by chondrocytes at temperatures above 39 degrees C, while induction of synthesis of a 110,000 MW HSP only occurs at temperatures of 45 degrees C or greater. These differences in critical temperatures for induction, and data showing differences in kinetics of induction and repression of synthesis, suggest that there are differences in the mechanism of induction of the two HSPs. The duration of HSP synthesis and inhibition of synthesis of normal cellular proteins is directly proportional to the duration and magnitude of the temperature rise. Possible relationships between these new findings and the initiation and progression of degenerative joint disease are discussed.

Contact pressures from an instrumented hip endoprosthesis.

A pressure-measuring Moore-type endoprosthesis was implanted in a seventy-three-year-old patient who had sustained a displaced fracture of the femoral neck. The measurement and telemetry of contact pressures in the hip began in the operating room, and data were acquired periodically for more than thirty-six months. Unexpectedly high localized contact pressures between the acetabular cartilage and the prosthesis were recorded. Early in the period of recovery, activities such as using a bedpan or performing isometric exercise produced pressures that were close to those recorded during normal walking. The highest pressure, eighteen megapascals, was recorded one year postoperatively, while the patient was rising from a chair. High pressures occurred in the superior and posterior aspects of the acetabulum.

The frequency content of gait.

We address amplification of noise in double differentiation of position histories for dynamic analysis of gait. Measurements of the frequency domain characteristics of signal and noise are required to quantitatively assess errors in raw, filtered, and dynamic gait data. The results of a simple technique to determine the frequency content of gait using a population of 12 subjects and a total of 30 gait records is presented.

Limitations of the continuum assumption in cancellous bone.

Most existing stress analyses of the skeleton which consider cancellous bone assume that it can be modelled as a continuum. In this paper we develop a criterion for the validity of this assumption. The limitations of the continuum assumption appear in two areas: near biologic interfaces, and in areas of large stress gradients. These limitations are explored using a probabilistic line scanning model for density measurement, resulting in an estimate of density accuracy as a function of line length which is experimentally verified. Within three to five trabeculae of an interface, a continuum model is suspect. When results as predicted using continuum analyses vary by more than 20-30% over a distance spanning three to five trabeculae, the results are suspect.

Modelling of the biomechanics of posture and balance.

A technique for studying the relationship of posture to balance has been developed. To investigate this relationship quantitatively, the human body was treated as consisting of 11 rigid body segments, each with six degrees of freedom. A bilateral Selspot II/TRACK data acquisition system provides position and orientation kinematic data for estimation of the trajectories of the individual body segment centers of gravity. From these, the whole body center of gravity is estimated and compared to concurrent force plate center of force data. Center of gravity and center of force excursions agree where dynamics are not significant. The technique may be employed to study quiet stance, response to postural disturbances, or the initiation and coordination of complex movements such as gait.

Optical verification of a technique for in situ ultrasonic measurement of articular cartilage thickness.

Several investigators have used pulse-echo ultrasonics to measure the thickness of articular cartilage in situ. The underlying assumption in all measurements was that the second reflection used in thickness calculations was from the calcified-cartilage/cartilage boundary (tidemark). To investigate this assumption, the thickness of 24 cartilage plugs excised from a human femoral head was measured both ultrasonically and optically. Measurements established that the second reflection was from the tidemark and validated the ultrasonic technique as a method of mapping the thickness distribution of articular cartilage in synovial joints in situ.

Mechanics of a constrained chair-rise.

A sit-to-stand task is analyzed by a method which estimates the segmental and whole body center of mass (CoM) kinematics and kinetics using bilateral whole body kinematic data from nine healthy young female subjects. The sit-to-stand, or chair-rise, task is constrained with regard to chair height, pace, initial lower limb position and arm use. The chair-rise maneuver is divided into four phases; (1) the flexion momentum phase; (2) the momentum transfer phase; (3) the vertical extension phase; and (4) the stabilization phase; the first three are examined in detail here. The momentum transfer phase, which immediately follows lift-off from the seat of the chair, is the most dynamic portion of the event, demanding a high degree of coordination. This maneuver is analyzed in order to determine if trunk movement is used only to position the body center of gravity or if the trunk motion generates momentum which is important during the brief but critical period of dynamic equilibrium immediately following lift-off from the chair. Our evidence points to the latter case and indicates that inter-segmental momentum transfer is possible during this period.

Hip muscle co-contraction: evidence from concurrent in vivo pressure measurement and force estimation.

The biomechanical literature over the past three decades reports direct measurements of human hip joint contact forces from instrumented implants which in general are quite different than estimates of contact forces based on external kinematic-ground reaction force data and inverse Newtonian analyses. Because direct physical measurement establishes veridical values in science, the higher analytical estimates may overestimate the balanced muscle force increments in agonist-antagonistic muscles about the joint (called co-contraction) which control joint impedance and contribute to joint stability. We studied the extent of muscle co-contraction by comparing in vivo endoprosthesis pressure measurements on hip articular cartilage and intersegmental force estimations from concurrent kinetic-kinematic data. Muscle co-contraction was evident from pressure magnitudes higher than those consistent with external data, from pressure rises before foot-floor contact, and substantial differences in the locations on the acetabulum of the highest pressures compared with the corresponding force vectors estimated from external data. Therefore, joint force and pressure inferences from external kinematic and kinetic data, without corroborating direct, internal measurements, should be made with more caution than is evident in the current literature.

Whole-body movements during rising to standing from sitting.

Rising to a standing position from a sitting position is one of the most important activities of daily life. We present a total-body analysis of rising from a chair as performed by nine healthy individuals under controlled conditions. We describe four phases of this activity. Phase I is a flexion-momentum phase used to generate the initial momentum for rising. Phase II begins as the individual leaves the chair seat and ends at maximal ankle dorsiflexion. Forward momentum of the upper body is transferred to forward and upward momentum of the total body. Phase III is an extension phase during which the body rises to its full upright position. Phase IV is a stabilization phase. Kinetics and kinematics of the phases are analyzed. The phases are differentiated in terms of momentum and stability characteristics. Clinical implications of the mechanics of rising are discussed.

Exercise and gait effects on in vivo hip contact pressures.

Virtually all hip rehabilitation programs include exercise for muscle force development. The specific effects of various exercise modes on the hip joint itself are unknown. We will report on the effects of common exercise modalities on in vivo hip pressures. Four years prior to data collection, a pressure-instrumented Austin-Moore-type endoprosthesis was implanted in an otherwise healthy 73-year-old woman with a traumatic right hip fracture. Hip pressures during various experimental maneuvers were recorded periodically over a 5-year period. We compared measurements of peak pressure and rate of pressure rise obtained during gait with those obtained during isokinetic, isometric, and isotonic lower-limb exercises. Maximal exercise generated greater peak pressures than did gait, and tripling the angular velocity during exercise roughly tripled the rate of pressure rise. Torque production and resultant in vivo hip pressures varied directly during all experiments. Peak pressures and rate of pressure rise apparently can be controlled by varying the subject's exertion. The results reported are from a single subject; therefore, little generalizability is possible for these data. We suggest, however, that articular pressures may be important to rehabilitation planning; these data provide a direct insight into this potentially important exercise prescription consideration.

In vivo acetabular contact pressures during rehabilitation, Part I: Acute phase.

The authors conducted a two-part study to compare in vivo acetabular contact pressures during the acute and postacute phases of rehabilitation. This report compares in vivo acetabular contact pressures generated during selected "inpatient" rehabilitation activities and their relationship to pain, range of motion, and other clinical indicators. A pressure-instrumented Moore-type endoprosthesis was implanted in a 73-year-old woman who had sustained a femoral neck fracture. Acetabular contact pressures during the first 2 weeks after surgery were rank-ordered. Clinical data, including range of motion, manual muscle test grade, use of pain medication, and independence in gait, were collected simultaneously. Acetabular pressures did not follow the predicted rank order corresponding to the commonly prescribed temporal order of inpatient rehabilitation activities. Isometric hip extension and active hip flexion generated the highest pressures of all the studied activities, including those measured during gait activities. Isometric exercises, therefore, may not be entirely benign preparation for ambulatory activity. Clinical data did not correspond with peak pressure data, suggesting that observed responses to rehabilitation may not be dependable criteria for progressing the acute hip rehabilitation protocol. We discuss applications for rehabilitation programs based on hip contact pressure data as an initial attempt to formulate more defensible rehabilitation approaches for patients with acutely painful hips.

In vivo acetabular contact pressures during rehabilitation, Part II: Postacute phase.

The authors conducted a two-part study to compare in vivo acetabular contact pressures during the acute and postacute phases of rehabilitation in a single subject with a pressure-instrumented femoral prosthesis. This report compares six common hip rehabilitation activities for resultant in vivo hip pressure magnitudes during the first 5 years after discharge from an acute care hospital. These activities were full, partial, touch-down, and non-weight-bearing ambulation and isometric hip abduction and straight-leg-raising exercises. A pressure-instrumented femoral endoprosthesis implanted in a 73-year-old woman who had sustained a femoral neck fracture provided data for the activities. The activities were rank ordered and compared over time according to peak pressure magnitude. Prescribed weight bearing and exercise type were not good predictors of hip peak pressures in this patient. Maximum pressures occurred by 1 year postdischarge for most activities, with a tendency to stabilize or decline thereafter. Resisted isometric hip abduction exercise demonstrated the most variation over time. The results suggest that hip pressures may be limited by controlling muscle force and movement velocity during postoperative hip rehabilitation activities.

Use of bone trabeculae to establish positive identification.

Radiographic examination of 42 adult distal left femora and 38 proximal left tibiae revealed that no two bones were identical in the pattern and appearance of the trabeculae. In each case, a minimum of four distinct osseous features was easily visible on radiograph. The results indicate that radiolucencies and radiodensities in the distal femur and proximal tibia are valid individualizing features for establishing a positive personal identification in human remains.

A blue encrustation found on skeletal remains of Americans missing in action in Vietnam.

A blue encrustation was found on the repatriated remains of three U.S. Servicemen listed as missing in action (MIA) from Vietnam after 28 years. The identification and origin of the blue material was determined. Scanning electron microscopy with energy dispersive analysis and powder X-ray diffraction identified the material as the mineral vivianite, Fe3 (PO4)2.8H2O. Vivianite has been found often associated with fossilized bone and teeth, but this example is unusual in that it is only the second published forensic example of vivianite growing from human bone after such a short period of time. The presence of vivianite provides information leading to a more complete and accurate understanding of the taphonomic process associated with American MIA remains.

A method for siding and sequencing human ribs.

Siding and sequencing (that is, putting in anatomical order) human ribs are essential to the proper examination and documentation of injuries to the chest. The paucity of information regarding sequencing nonfleshed human ribs makes it particularly difficult for physical anthropologists and medicolegal authorities to differentiate the midthoracic ribs. It was found that ribs could be accurately sequenced without the aid of a comparative skeleton using such features as maximum (relative) rib length, the size and shape of the articular facets, the distance between the articular facets and rib angle, and the height of the rib heads relative to one another.

Positive personal identity of skeletonized remains using abdominal and pelvic radiographs.

Premortem and postmortem radiographs of the chest and abdomen are often available for comparison and provide a basis for making or rejecting an identification. The case reported here exemplifies the way that individualizing features, such as contours of bony elements, skeletal anomalies, and radiodensities and radiolucencies, are used in establishing personal identity.