Abstract
The objective of this study is to compare three dimensional (3D) postoperative motion between metal and ceramic bipolar hip hemiarthroplasty for femoral neck fracture.
Materials and Methods
This study was conducted with forty cases (20 cases of metal bipolar hemiarthroplasty (4 males, 16 females), 20 cases of ceramic bipolar hemiarthroplasty (2 males, 18 females)) from November 2012 to November 2014. Average age was 80.8±7.5 years for the metal bipolar group and 79.3±10.5 years for the ceramic bipolar group. We obtained motion pictures from standing position to maximum abduction in flexion by fluoroscopy then analyzed by 2D–3D image matching method. The motion range of the “Shell angle”, “Stem neck angle” and the “Stem neck and shell angle” has been compared between the metal bipolar group and the ceramic bipolar group (Fig. 1).
Results
Metal bipolar showed greater variability of the Stem neck angle and Shell angle than ceramic bipolar. Six of the twenty cases reached unilateral oscillation angle of 37 degrees in metal bipolar. In other words, 30% of metal bipolar group revealed neck-shell impingement. No case reached oscillation angle of 58 degrees in ceramic bipolar group. There was no significant difference between the metal bipolar group and the ceramic bipolar group with respect to the difference of minimum and maximum angle of Stem neck angle (movement range of the stem neck) and Shell angle (movement range of the bipolar cup). On the other hand, difference of minimum and maximum angle of the Stem neck and shell angle (movement range of the inner head) was significantly greater in the metal bipolar group than the ceramic bipolar group. Movement, range of bipolar shell was significantly greater than that of inner head in both groups (Table 1).
Discussion
The present study is the first report using 2D–3D image matching method in bipolar impingement. From the result of our study, bipolar shell moves greatly against the acetabular cartilage for both metal bipolar and ceramic bipolar, and the range of movement of the outer shell was significantly greater than the range of movement of the inner head. It indicates that most of the movement actually occurs between outer shell and acetabular cartilage, despite bipolar prosthesis having a double bearing function intrinsic to the design.
Impingement between the shell and the stem neck was found six of twenty cases with metal bipolar group and no impingement occurred with ceramic bipolar group. The present results showed that the ceramic bipolar has the possibility to avoid the characteristic complications of the bipolar caused by the wear debris produced by impingement.
In conclusion, the metal bipolar group's inner head's range of movement was greater than the ceramic bipolar group. The impingement between stem neck and shell occurred in the 30% of metal group patients. On the other hand, there were no impingement cases for the ceramic bipolar group. We expect good long term clinical result and expansion of the indication as the ceramic bipolar may reduce the typical bipolar related complication.
