The stabilising effect of atmospheric pressure on the hip joint is a fact, which was proved in 1836/37 by the Weber brothers, who conducted convincing experiments with human cadaveric hip joints. Nevertheless, the investigation into this relationship continues until today. We repeated and reproduced their experiment published in 1837 which irrefutably proved the stabilising effect of atmospheric pressure on the hip joint. The surgical application is of the utmost importance in the field of hip arthroplasty. Careful handling and reconstruction of the capsula, the use of size-adapted large hip balls as well as the intra-articular drainage provide the basis for maintaining the optimal mechanical environment and avoiding postoperative dislocation. Due to the variation in quality and anatomic characteristics of cadaveric hip specimens, we decided to use standardised model joints for further experiments.
The traction force required for dislocation agreed closely to the expected precalculated SPR values of 58.6 N (A), 76.4 N (B) and 96.7 N (C), which proves the joint stabilising effect of AP in the presence of the essential prerequisites (spherical ball articulating in a hemispherical socket, hermetically closed joint capsule and/or labrum, which contains a small amount of fluid and excludes air). The measured SPR was directly proportional to the square of the joint diameter. Indirectly, it was concluded that the dislocation work at rest is directly proportional to the joint diameter cubed. Consequently, the risk of dislocation after total hip arthroplasty (THA) can be reduced by applying bigger, size-adapted hip balls, whose diameter grows according to the outer diameter of the cup. The increasing range of motion is a favourable side-effect. With careful reconstruction of the capsule and insertion of an intracapsular drain, the risk of dislocation in the early postoperative period could be furtherly reduced. Theoretically, artificial labra could be a useful alternative to augment joint stability in THA with a high dislocation tendency instead of constrained liners.
Enchondroma is the second most common benign bone tumour and the most common tumour affecting the bones of the hand. In the hand, they are most frequently found in the proximal phalanges. The case presented here is that of an expansive enchondroma in the distal phalanx of the thumb, which is rare. By operative treatment (curettage, reduction plastic and cancellous bone allografting) we were able to correct the deformity of the distal phalanx and the thumbnail almost completely, as well as improving the stability and achieving a good cosmetic result.
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