The best outcomes were observed in joints with “centred” degeneration and cuff destruction. Preservation of a satisfactory centring of the cup avoided pain and enabled a mean anterior elevation of 1112.3° with a weighted Constant score of 90.5%. For early excentred degeneration, preservation of the glenoid bone stock prevented perfect joint congruency leading to excessive lateralisation of the humerus: 20% of the shoulders remained painful and anterior elevation reached 68° with a weighted Constant score of 56%. Paradoxically, results were better in patients with severely excentered degeneration. “Acetabulation” of the shoulder preserved joint congruency and lengthened the lever arm of the deltoid by medialisation and lowering of the centre of rotation. Full pain relief was achieved in all such cases, with anterior elevation at 86° and a weighted Constant score at 78%.
There was a correlation between the anatomic presentation and function, especially evident for the Méary-Tomeno line which must be re-established. While we obtained spontaneous correction of the compensating frontal and sagittal deformations of the hindfoot, specific procedures were required to alleviate claw toes and equinism. It is also important to preserve the Lisfranc space and the Chopart space. The corrective capacity of tarsectomy is limited. To achieve satisfactory anatomic and functional results, tarsectomy must be reserved for moderate pes cavus involving a sufficiently mobile forefoot with moderate and reducible calcaneal varus where the primordial joints can be saved.
Three types of biomechanical behaviour were also observed for rotation movements: a “chronological “ behaviour was observed for 15 prostheses, via extraprosthetic mobility in all. Mean external rotation was 37.33° and mean internal rotation was 6.53 points. An “anarchic” behaviour was observed in 16 prostheses with a random proportion of intra- and extraprosthetic mobility. Mean external rotation was 8.75° and mean internal rotation was 4.25 points. For shoulders with “chronological” or “anarchic” behaviour, the mean external rotation (p = 0.002) and the mean internal rotation (0.04) were statistically better than shoulders with “truncated” behaviour.