Abstract
Introduction
Neck and cup impingement resulted in producing larger amount of wear and risk for dislocation after total hip arthroplasty. DDH had more complex to adjust combined cup and femoral neck anteversion during surgery. Dislocation is the second most prevalent complication in total hip replacement with a 2–4% incidence. These resulted in significant financial burden to health care system. Sixteen million US dollars or more cost had in Japanese health insurance system every year. Purpose of this study was to evaluate neck-cup impingement with neck changeable M/L taper Kinectiv stem for DDH patients.
Materials & Methods
Single surgeon's series were analyzed neck cup impingement of 1152 primary total hip surgeries with DDH. 269 hips in men, surgical approach were 754 mini-one antero-lateral, 284 mini- Watson-Jones, and 114 Hardinge. Acetabular cups were seated 20 degrees anteversion. Kinectiv Stem (Zimmer, Warsaw, IN) was inserted manually with standard technique. Femoral head selection was performed 26mm CoCr basis. 32mm were used for 75 years old or more, and 36mm were 80 years or older. First trial was performed with straight type of neck and 26mm femoral head based on preoperative templating. At neck and head trial to evaluated antero-superior impingement with “flex+add.+IR” and postero-inferior impingement with “ext.+add.+ER”. If the neck and cup impingement occurred even if no dislocation, necks were replaced counter version or larger offset.
Results
Neck trial was 2 to 3 times during surgery (ave. 1.9). Version was changed 395(33%) cases. Surgeon selected larger offset in 246, 235 longer length, 99 shorter length. Larger offset with longer length were used in 229 (20%), 117 (10%) had larger offsets and shorter length compared to 2D templating before surgery. We had 2 dislocations (0.48%) with10 degree extended lip PE (2/359: 0.56%) and 2 for flat PE liner (2/793: 0.25%) fixed with manual reduction. All were using very short neck (E; minus 4 in length and S; minus 4 in length, plus 4 in offset) with smaller arc of movement type because of tight to redact compared expected proper positions. All dislocated cases were revised with larger femoral head. Our first series of 1500 Versys system with 10 degree extended lips had 0.74% (14/1880) (2004–9) dislocation rate. Kinectiv neck changeable stem had 66% reduction of dislocation rate (p<0.05). Averaged hospital stay was 7 (3–12) days.
Discussion
One Kinectiv stem had 60 variety of necks based on 4 mm head center difference. Large amount of variation especially anteverted or retroverted neck selection might reduce neck-cup impingement compared to other straight type of femoral stems. Combined anteversion is very important especially in DDH patients, because of larger femoral anteversion. Proper offset and leg length are also very important issues for any type of patients. This type of stem had more advantages than straight type monolithic stems to reduce wear and dislocation caused by impingement. Care must be taken for reducing impingement with selecting shorter length or offset during surgery. Lower dislocation rate are very effective to health insurance system.
