F L. Drijber

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Malreduction and malalignment (malunion) of tibial fractures is often an unfortunate consequence of their treatment with half-frame external fixation devices. This problem is especially apparent in fractures with poor or absent bony apposition following proper surgical reduction. The increased demands placed on the fixator by weight bearing, escalate the incidence and severity of this complication. Therefore, this study sought to investigate a possible cause of this problem in the Hoffmann fixator, namely slippage in the universal joints, and to establish if any solution could be instituted to resolve or alleviate this slippage.;An initial analysis was performed to determine the loads which would cause an individual joint to slip at each of its interfaces of motion. These values were tested against the theoretical loads these same joints bore when an entire frame was tested to failure to determine if the earlier experiments had predictive power. Next, a joint modified to reduce slippage was tested in a similar manner to establish if it would better enable the fixator to bear functional loads. It was then determined if these slippage values were sufficient to enable the Hoffmann half-frame fixator to withstand functional weight-bearing.;The slippage values of the individual joint were found to be predictive of their performance within a total frame. The standard Hoffmann universal joint could not be expected to bear functional loads in a half-frame configuration without slippage occurring. The modified joints decreased the slippage problem in the joint and indicated certain Hoffmann half-frame configurations could protect against joint slippage under functional loads for some tibial fracture types.;Thus, universal joint slippage in Hoffmann half-frame fixators leading to frame failure and possible subsequent fracture malalignment could account for some of the malunion seen in tibial fractures bearing functional loads. Standard universal joints cannot be expected to bear functional loads for the tibia without failure. Half-frame configurations constructed with modified universal joints can be expected to withstand these loads in certain tibial fracture types, but based on this study, there appears to be little likelihood of half-frame configurations protecting against joint slippage and its subsequent complications in all types of tibial fractures.



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