EFFECT OF INCREASING HEAD DIAMETER ON THE RANGE OF MOTION AND STABILITY IN TOTAL HIP ARTHROPLASTY

Abstract

Introduction: Experimental studies in anatomic full size hip models indicate that larger femoral heads offer potential in providing greater hip range of motion and joint stability. We studied the effects of increasing head diameter from 28mm to 36 mm in total hip replacement (THR) on the range of flexion and abduction.

Methods: 243 patients who underwent primary total hip replacement with S ROM prosthesis between July 1996 and June 2004 were studied. 151 patients (77 male and 74 female) underwent THR with 28 mm head and 92 patients (38 male and 54 female) underwent THR with 36 mm head. The range of flexion and abduction were studied and statistical analysis was performed using the Student t-test. We monitored the dislocation rate in both groups.

Results: The mean flexion is 87.0 for the 28 mm group and 89.6 for the 36 mm group. The mean abduction is 27.77 and 27.98 for 28mm and 36mm groups respectively. Even though there is a slight increase in the mean flexion and abduction from the 28mm to 36mm group, this increase in not found to be statistically significant. For flexion (2.6 (−0.85 to 3.2); p=0.377), and for abduction (0.02 (−2.37 to 1.94); p=0.847). Three hips dislocated in the 28mm group (2%) but none of the hips in 36mm group has dislocated.

Discussion: Even though experimental studies indicate improvement in range of motion with increasing head diameter in THR, this effect is not reflected in our clinical study. But there is improvement in the joint stability by using a prosthesis with larger head diameter as evidenced by a reduction in the dislocation rate.