Abstract
Introduction
The acetabular cup should be properly oriented to prevent dislocation and to reduce wear and leg length discrepancy. Despite advances in surgical techniques and instrumentation, achieving proper cup placement in total hip arthroplasty (THA) is challenging with potentially large variations of cup position and limited accuracy. We evaluated whether cup placement on anatomical location ensured original center of rotation (COR) and surgeon's experiences of THA reduced variations in acetabular component positioning.
Methods
We retrospectively reviewed 145 patients (145 hips) of unilateral THAs with normal contralateral structures of acetabulum and femoral head. All surgeries were performed using the modified posterolateral approach that preserves short external rotator muscles. All of the 145 THAs were performed by two surgeons, who were in the same teaching hospital, but had differences in surgical experience and expertise for THA. The patients were divided into two groups based upon surgical experience: (1) the highly experienced surgeon's group: who had previously performed over 1000 THAs (YSK, 101 hips), and (2) the less experienced novice's group: who had performed fewer than 30 THAs (YWL, 44 hips). Real vertical distances, from the COR to the inter-tear drop line, and the real horizontal distances, from the COR to the lateral wall of the tear drop, were measured preoperatively using picture archiving communication system (PACS) based precise method. Postoperative ones were measured and equalized by use of a magnification marker placed on preoperative plain radiographs. And cup inclination was measured directly on the AP radiographs and anteversion was calculated by trigonometric functions. The patient's mean age was 52.1 years (range, 20–86).
Results
The difference between preoperative and postoperative vertical distances of COR was mean 2.8±2.6 (range. −3.1–9.9) for the surgeon groups combined; it was mean 2.5±2.3 (range, −2.6–7.4) for the highly experienced surgeon and mean 3.7±2.9 (range, −3.1–9.9) for the less experienced surgeon(P = 0.009). The difference of horizontal distances of COR was mean 2.6±2.9 for the surgeon groups combined; it was mean 2.5±2.7 (range, −3.9–9.1) for the highly experienced surgeon and 2.8±3.3 (range, −2.8–10.2) for the less experienced surgeon(P = 0.87). The cup inclination was mean 43.4±7.6 (27.2–60.4) for the surgeon groups combined; it was mean 40.7±6.4 (range, 27.2–56.5) for the highly experienced surgeon and mean 49.4±6.5 (range, 29.2–60.4) for the less experienced surgeon (P = 0.001). The radiologic anteversion was mean 16.1±6.5 (range, 3.7–34.3) for the surgeon groups combined; it was mean 15.7±6.1 (range, 3.7–32.4) for the highly experienced surgeon and 17.2±7.2 (range, 5.1–34.33) for the less experienced surgeon (P = 0.194). 3 hips (7%) were dislocated in the novice's group, whereas none from the expert's group was dislocated.
Discussion
In spite of the effort to restore anatomical COR, the cup COR tends to be located superiorly and medially compared to the original COR due to the influence of acetabular component and intended medialization of cup placement. Nevertheless, our findings suggest that a surgical experience could reduce variations in acetabular component positioning.
