Purpose: Two questions arise after metatarsophalangeal hallux arthrodesis: what are the 3D changes observed when walking on flat ground ? and is the arthrodesis compensation essentially at the talocrural or interphalangeal level ?

Material and methods: Our series included twelve patients (ten women and two men) mean age 60.7 years. Nine patients had unilateral arthrodesis and three bilateral arthrodesis. The optoelectronic exploration was conducted barefoot. The patients wore underclothes and 27 reflectors. A miniaturised reflector was placed on the distal end of each hallux. Three valid recordings were made.

Results: General gait parameters and kinematic and kinetic values were unchanged (excepting nonsignificant maximal ankle dorsiflexion). On the arthrodesis side we observed: significant decline in propulsion force in the anteroposterior and vertical planes; significantly later heel lift-off; systematic anterior displacement of the ground reaction force of the metatarsophalangeal joint (not seen on the healthy side).

Discussion: We propose a coherent explanation of these observations. The kinetics of balance movement under the head of the first metatarsal head is changed. When the foot is flat on the ground, as the ankle balance movement occurs, the weight of the body is transferred earlier and massively to the forefoot. While in the healthy foot this occurs under the metatarsophalangeal joint of the great toe, in arthrodesis patients body weight is transferred under the interphalangeal joint of the great toe. The balance movement of the interphalangeal joint of the great toe occurs when the ankle balance movement is terminated. The centre of the balance movement is more distal and heel lift-off tends to occur later. During the propulsion phase, the greater lever arm limits the propulsion force, explaining the lesser peak force observed on the arthrodesis side. Use of reflectors on the distal end of the hallux demonstrated that the arthrodesis compensation occurs essentially at the interphalangeal level, exposing this joint to greater risk of degeneration.

Purpose: Despite the development of new imaging techniques (MRI, CT scan) longitudinal studies of total hip arthroplasty (THA) are still conducted with conventional radiographs. New techniques for conventional radiograpy such as luminous screens with memory raise the question of longitudinal study in patients with THA where the new screen-film might produce artefacts.

Material and method: This prospective study examined intermethod and interobserver agreement. Thirty-seven patients were included in the series from July 1st, 1998 and September 30, 1998. Each patient had a double radiography series: three plain films using the conventional technique (C) and three digitalized screen films (D). The C were taken with a 1/1 ratio on a Philips Diagnost 90 table and developed using the Kodak M6 method using a 36 x 43 cm cassette for the pelvic x-ray and a 24 x 30 cm cassette for the x-ray of the prosthetic hip. The D were made on the Philips Diagnost 90 table and developed with the Agfa ADC70 procedure on a memory screen with a 5 pl/mm spatial resolution for 36 x 43 cm for the pelvic x-ray and 28 x 35 for the prosthetic hip. The same operator performed the complete radiography series in the same patient (C and D). The images were read examining the cement/bone interfaces and the prosthesis/cement interfaces looking for the classical radio-lucent lines in the De Lee and Charnley sectors. The presence and the thickness of the radiolucent line were classed in three groups: no line, line less than 2 mm, line greater than 2 mm. For each patient, the films were placed in anonymous folders and two subgroups were selected at random for the readers (a radiologist and an orthopaedic surgeon) who did not read successively the same films for the same patient. The results were recorded with an Excel data sheet and the statistical analysis was done with the BMDP software.

Results: Thirty-seven patients were included (22 women and 15 men) with 40 THA. Mean age was 64 years (42–86). Mean follow-up of the THA was 25 months (2–248). Four patients had mechanical pain or deceased joint amplitude and 33 patients had no clinical sign. Only one lucent line was found measuring less than 2 mm in the 1st quadrant of the cup and the 3, 4, and 5 zones on the AP view and the 10, 11, 12 zones on the lateral view on the tail of the pros-thesis. In this study, the kappa value was less than 0.5 for the mean concordance according to the Landis and Koch classification. The Kappa was higher for the intermethod analysis irrespective of the reader, than for the interobserver analysis.

Discussion, conclusion: Independent readers of the two types of images (C and D) did not demonstrate any difference for cemented or noncemented prosthesis in a longitudinal study of THA. The reproducibility between the C and D techniques was small. However, our study only analysed a few of the numerous radiographic signs considered to favour loosening (stress shielding, lucent lines etc.…). However, the analysis of the Kappa results demonstrated mean concordance between the techniques better than mean concordance between observers.