Dislocation of the femoral head from the acetabular socket is a disturbing complication for both patient and surgeon. The incidence of femoral dislocations after primary total hip arthroplasties has diminished. Dislocations still do occur, particularly with inexperienced surgeons and following revisions. This retrospective review of 39 dislocations classifies the mechanical factors responsible for dislocations and proposes a protocol for care of these patients.
MATERIALS AND METHODSA computer-assisted search of hospital records disclosed 38 patients treated for 39 dislocating total hip arthroplasties; one patient had bilateral dislocations. In addition, 22 patients who did not have dislocations and who had normal functional recovery as defined by gait data were used as a control group to judge the limits of acceptable component positioning. These limits were compared with those established in the literature.'^^ Data reviewed from the charts were the patients' age, hip disease, prior operations on the involved hip, date of dislocation, reason for dislocation as identified at the time, and number of dislocations. Surgical reports were used to establish estimated femoral component position (when this was dictated). This information was collected From the for the patients had who dislocations and for the control group.Data obtained from roentgenograms were the vertical placement of the acetabular cup (theta angle); anteroposterior rotation of the cup (alpha angle); cup placement in relation to the anatomic position of the acetabulum in the pelvis; moment arm of the gluteus medius; femoral neck length; and position of the center of the femoral head. Alpha and theta angles of the acetabulum were measured by the techniques of Lewinneck et aL6 (Fig. 1); anatomic position of the acetabulum was measured by the method of Ranawat et al.' (Fig. 2); femoral neck length and center head measurements were made by the technique of Gore et al.' (Fig. 3).Cup placement was defined as superior if it was greater than 1 cm above the anatomic level or if the placement elevated the center of the femoral head 1 cm from its anatomic level. Femoral neck osteotomy was defined as excessive if the final femoral neck length was decreased by more than 1 cm from anatomic length. In none of these hips did a preoperative dislocation require excessive shortening of the femur (as with CDH). Soft tissue imbalance of the hip, ie., shortening of muscles and fascia, was considered to be present if either of the above problems existed and the trochanter had not been transplanted distally. Soft tissue imbalance also was identified if the transplanted trochanter retracted superiorly after wire breakage or escape from the wires. Both of these are referred to as trochanteric escape. The mechanisms for dislocation with soft tissue imbalance include impingement of the trochanter on the pelvis. This can occur on the posterolateral pelvis with extension and external rotation, and the hip can dislocate in extension. With flexion, adduction, and internal rotation,...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.