Neurovascular structures at risk from proximal locking of retrograde femoral nails
The Richards retrograde femoral nail (Smith and Nephew 1997) is inserted into the medullary canal of the femur via an entry point in the intercondylar fossa, just anterior the anterior cruciate ligament. This particular implant requires insertion of both proximal and distal interlocking screws for maximal axial and rotational stability. The distal screws are inserted lateral to medial in a relatively safe area of the lower thigh using an external guide. The proximal locking screws by contrast are inserted 'freehand' at the level of the lesser trochanter in an anteroposterior direction using X-Ray control. The proximal thigh contains many vital neurovascular structures and it is the proximity of the femoral nerves and vessels which is of significant concern due to the relative inaccuracy of the freehand technique (Riina et al 1998). Hypothesis This led me to my first null hypothesis that 'proximal anteroposterior locking screws of retrograde femoral nails can be inserted in the proximal end of the femur through the proximal thigh without damage to the nerves and vessels'. To test this hypothesis we proposed to: 1). Dissect the main nerves and vessels of the thigh and describe their position and relation to the lesser trochanter. 2). Place investigative drill holes in a modified anatomical procedure to imitate insertion of the proximal anteroposterior locking screws. 3). Dissect the proximal thigh to determine whether important anatomical structures are at risk of being damaged by the proximal anteroposterior locking screws. The preliminary results of this first investigation lead to a second null hypothesis:- That the nerves and vessels of the upper thigh are at risk from proximal locking screws inserted in a lateral to medial direction in the upper thigh. To test this hypothesis we propose to; 4). Plan dissections to compare lateral to medial locking with anteroposterior locking, for use with a redesigned nail. 5). Finally we proposed a modified clinical trial of the redesigned nail. This would involve attaching the redesigned nail to the side of a volunteer's thigh and taking X-Rays in theatre to determine whether the redesigned nail could be adequately screened to allow its use in practice.