Aplasia of the os odontoideum: Skeletal manifestation from Thailand.

Os odontoideum is a rare craniocervical abnormality of the axis resulting in absence (aplasia) of the dens and, possibly, dislocation of the atlantoaxial articulation. Skeleton 0202 from the Osteology Collection at Khon Kaen University, Thailand exhibits aplasia of the os odontoideum with torticollis, accompanied by an unusual constellation of skeletal features that include craniosynostosis, platybasia with mild basilar invagination, unilateral Kimmerle anomaly, disuse atrophy resulting in "wasting" of the upper and lower limbs, and marked stenosis of the right foramen transversarium of the axis. The remains of this individual provide anthropologists and clinicians the rare opportunity to study the combined effects of os odontoideum, craniosynostosis, torticollis, platybasia and skeletal atrophy in a known-identity individual from Thailand.

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.

Cartilage degeneration in relation to repetitive pressure: case study of a unilateral hip hemiarthroplasty patient.

In vivo acetabular contact pressures were measured over 32 months in an elderly man with a pressure instrumented hemiarthroplasty. After death, left (hemiarthroplasty) and right (control) acetabula were explanted. Cartilage thickness and degeneration were quantified from magnetic resonance imaging and histological analysis. Highest repetitive in vivo contact pressures during gait (4.5 to 6.5 MPa) were measured in the superior dome of the acetabulum and decreased at a rate of approximately 1 MPa per year after implant (R2 = 0.48, P < .001). Contact pressure magnitudes measured during gait correlated positively with regional histology score (R2 = 0.34, P < .0001) and negatively with cartilage thickness (R2 = 0.35, P < .0001). Although histology scores were typical of early osteoarthritis (histological grade of 4-6), there were no significant differences in overall histology score for the left and right acetabula (P = .23). We conclude that acetabular cartilage degeneration was explained, in part, by repetitive stress, but the degeneration did not appear to be mediated solely by articulation with the metallic endoprosthesis.

Perimortem calcaneal and talar fractures sustained in a military air crash in Vietnam.

The authors report on the skeletal elements of a minimum of 37 men who died in 1965 when their C-123 cargo airplane crashed into a mountainside in South Vietnam. Natural environmental processes reduced their bodies to skeletons; these osseous remains were recovered from the crash site nearly 10 years later. Among the remains were the calcanei and tali of at least 37 people. These bones, devoid of soft tissue, provide a rare opportunity to examine and document the pattern of perimortem fractures in multiple individuals who died in the same incident. This case also provides information on a range of variability of skeletal fractures that is unavailable in comparative skeletal collections, and that might be overlooked with radiography or during physical examination.

Hip biomechanics during gait.

The literature is devoid of complete descriptions of hip biomechanics during gait. We present for the first time simultaneously acquired in vivo acetabular contact pressures, ground reaction forces, kinematics, hip torques, and electromyographic (EMG) activity during gait with and without a cane from an 85-year-old male with a left instrumented femoral head prosthesis. Highest acetabular contact pressures occurred in all gait trials at the posterosuperior acetabulum, just prior to peak EMG, adductor torque, and ground reaction force during late stance phase. Contralateral cane use reduced both peak acetabular contact pressure and gluteus medius EMG but not adductor torque or ground reaction force. These data identify a small area of high acetabular and femoral head stress that could occur during each of a human's millions of gait cycles annually and indicate that muscle activity, rather than solely body weight, drives hip loading, Clinicians who desire to limit hip loads should reduce both hip muscle contraction and weight bearing in late stance.

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.

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.

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.

Hip stress during lifting with bent and straight knees.

"Correct" body mechanics during lifting are believed to protect the back by employing knee and hip flexion while keeping the back straight. Lower limb joint stress, however, has been largely ignored. We compared hip cartilage contact stress during "leg lifting" with "back lifting" (lifting with bent or straight knees, respectively) in a subject fitted with a pressure instrumented hip endoprosthesis. Synchronized pressure data and whole-body kinematics and kinetics were collected simultaneously while the subject lifted an 11.8 kg mass from the floor to waist level. The highest pressure, 13.7 MPa, occurred during leg lifting at the antero-lateral femoral head transducers opposed at maximum hip flexion by the postero-superior quadrant of acetabular cartilage. In back lifting, the highest pressure, 11.5 MPa occurred in the supero-lateral aspect of the head, which during hip extension was opposed by the posterior quadrant of the acetabulum. Maximum pressures and hip torques occurred simultaneously with peak hip flexion, during the initial lifting of the burden from the floor. Acetabular contact pressures during leg lifting were on average twice as great as during back lifting, and both techniques generate much greater hip stress than gait (typically 4-6 MPa). Degenerative changes in the articular surface of the acetabulum occur primarily on the postero-superior aspect, corresponding to the locations of peak contact pressures in the present in vivo data. Thus leg lifting puts more stress on the postero-superior region, and probably contributes to more hip cartilage degeneration, than does back lifting. We conclude that although leg lifting may mechanically protect the back, it substantially increases hip cartilage stress.