Biomedical subjects
Publications and source records attributed to T M Turner.
A craniolateral approach to the canine elbow was developed. It provides for direct visualization of the distal humeral articular surface, thus facilitating precise repair of condylar fractures. Inasmuch as the primary supporting ligamentous and tendinous structures are not incised, a stable postoperative joint with normal range of motion can be achieved.
A major problem threatening the long-term integrity of total hip replacement is the loss of proximal bone often found around noncemented stems in the long term. It is generally accepted that 'stress shielding' is the cause for this problem: after implantation of the prosthesis the surrounding bone is partially 'shielding' from load carrying and starts to resorb. One of the proposed answers to this problem is the application of press-fitted stems. These smooth-surfaced implants are thought to provoke higher proximal bone loading, and, hence, less stress shielding than bonded implants, because they are wedged into the femur every time when loaded. However, in a two-year experiment in dogs, similar amounts of resorption of the proximal cortex were found around press-fitted and bonded implants. The question arises how similar resorption patterns can develop under completely different stress conditions, and whether this phenomenon can be explained by adaptive bone remodeling theories based on Wolff's law. In the present study an answer was sought for this question. An advanced iterative computer simulation model was used to analyze the remodeling process in the animal experiment. Three-dimensional finite element models were constructed from the animal experimental configuration, in which smooth, press-fitted stems were applied unilaterally in the canine. The FE model was integrated with iterative remodeling procedures, validated in earlier studies. In the model an appropriate non-linear representation of the loose bone-implant interface was realized, also capable of simulating the proximal interface gap that was found around the uncoated implants. The simulation models predicted similar amounts of proximal bone loss and distal bone densification as found in the animal model. Hence, the cortical bone loss could indeed be predicted by the strain-adaptive bone remodeling theory. By unraveling the simulation process, the question stated above could be answered. Densification of the distal bone bed during the initial remodeling process was found to cause reduced axial stem displacement (elastic subsidence), decreasing the wedging effect of the stem and, hence, decreasing the loading of the proximal bone, resulting in proximal bone loss. Hence, whereas in the case of bonded stems the proximal resorption process develops monotonously to a new equilibrium, the process around smooth, press-fitted stems develops nonmonotonously. This is due primarily to the unbonded interface conditions and the development of a proximal fibrous membrane. The remodeling process then gradually causes the stem to be jammed in the distal diaphyses (proximal 'stress bypass').
The efficacy of partial carpal arthrodesis was evaluated retrospectively in 39 dogs (45 carpi) with severe sprains of the middle carpal joints, the carpometacarpal joints, or both. The carpometacarpal joint was the most frequently injured joint. Jumping or falling from heights was the cause of injury in 49% of these animals. Of the 25 owners who responded to a mailed questionnaire (mean follow-up, 32 months), all stated their animal had improved or greatly improved after partial carpal arthrodesis and all were pleased or very pleased with the final surgical result. Hyperextension persisted in 11% of the cases and degenerative joint disease of the antebrachiocarpal joint was present in 15.5% of the cases. No dogs with partial carpal arthrodesis required panarthrodesis at a later date.
A radiographic analysis of 483 Charnley total hip arthroplasties performed from July 1970 to November 1975 demonstrated that 13% of the hips had lysis of the medial femoral neck. The findings suggest that the lysis of the medial femoral neck is significantly reduced if the femoral stem is oriented in a valgus or neutral position and with at least 5 mm of cement separating the stem of the prosthesis and the medial cortex of the femoral neck.