FEACTUEES OF THE PATELLA. 97 



fracture is as a rule immediately distal to the attachment of the 

 heads of the gastrocnemius. The consequence of this is that the 

 lower end of the upper fragment may be drawn backwards and 

 downwards, and press upon the vessels, whilst the epiphysis itself 

 may be dislocated forwards. 



Fractures of the Patella. The patella is covered in front by 

 the skin, superficial and deep fasciae, and a tendinous expansion 

 from the quadriceps. Posteriorly it is coated with articular car- 

 tilage save at its tip, where is the attachment of the ligamentum 

 patellae. Hence it follows that all fractures of the patella which 

 traverse the whole thickness of the bone, except its lowest part, 

 necessarily lacerate the aponeurosis anteriorly and implicate the 

 joint behind. 



The position of the patella, placed as it is between the insertion 

 of the quadriceps above and the patellar ligament below, renders 

 it liable to a very great longitudinal strain particularly in such 

 efforts as to save oneself falling after missing a step in ascending 

 the stairs. Hence this bone is more frequently broken by that 

 form of indirect violence known as muscular than any other in 

 the body. Its exposed position on the summit of the knee also 

 renders it liable to direct violence, which may also lead to its 

 fracture. 



In the lesion by muscular action it is somewhat doubtful whether 

 the transverse fracture which occurs is due to leverage, the patella 

 resting by its posterior surface on the trochlear surface of the 

 femur as on a pivot. If the movement of the knee in flexion and 

 extension is accurately observed, it will be found that at no time 

 is any part of the patella really unsupported. It glides upon, but 

 always remains co-apted to, the articular surface of the condyles 

 of the femur. Hence it follows that the common transverse 

 fracture is the outcome of an almost pure longitudinal strain, 

 which in the great majority of cases breaks the bone, but may 

 tear the quadriceps tendon at or near its insertion, may lacerate 

 the ligamentum patellae, or may even drag off the tubercle of the 

 tibia. In most instances where bone, tendon or ligament has to 

 bear a strain, the breaking force is least readily borne by the bone, 



C.A.A. 7 



