Widmer K-H, Majewski M
Laboratory for Orthopaedic Biomechanics, University of Basel, Switzerland.
Clin Biomech (Bristol). 2005 Aug;20(7):723-8. doi: 10.1016/j.clinbiomech.2005.04.003.
Biomechanical analysis and clinical experience reveal that offset total hip stems increase soft tissue tension and reduce the risk for dislocation in total hip arthroplasty. Most of these stems have a smaller neck-shaft-angle to increase the offset. This study investigates if changing the neck-shaft-angle has an impact on how cup and stem should be positioned with regard to range of motion.
A mathematical model of a total hip arthroplasty was developed to analyze range of motion until impingement between cup and neck. Range of motion was determined for each combination of neck-shaft-angles and additional parameters like cup inclination, cup anteversion, stem antetorsion, head/neck ratio and design of the cup opening.
A maximized range of motion is achieved for neck-shaft-angles between 125 degrees and 131 degrees . Reducing the neck-shaft-angle by one degree requires reducing the cup anteversion by about 2 degrees and increasing the cup inclination by 0.45 degrees . Stems with neck-shaft-angles more than 135 degrees are not recommended when the head/neck ratio is 2.3 or less.
Stems with a reduced neck-shaft-angle for an increased offset should be coupled with cups that are inclined slightly higher and less anteverted as compared to a standard stem. Precise recommendations for optimal component positioning can only be given for a specific prosthesis system regarding all parameters.
生物力学分析和临床经验表明，偏心全髋关节柄可增加软组织张力并降低全髋关节置换术中脱位的风险。这些柄中的大多数具有较小的颈干角以增加偏心距。本研究调查改变颈干角是否会对髋臼和股骨柄在活动范围内的定位方式产生影响。
建立了全髋关节置换术的数学模型，以分析髋臼和股骨颈之间发生撞击前的活动范围。针对颈干角与其他参数（如髋臼倾斜度、髋臼前倾角、股骨柄前倾角、头颈比和髋臼开口设计）的每种组合确定活动范围。
颈干角在125度至131度之间时可实现最大活动范围。将颈干角减小1度需要将髋臼前倾角减小约2度并将髋臼倾斜度增加0.45度。当头颈比为2.3或更小时，不建议使用颈干角大于135度的股骨柄。
与标准股骨柄相比，为增加偏心距而减小颈干角的股骨柄应与倾斜度稍高且前倾角较小的髋臼相匹配。只有针对特定假体系统的所有参数才能给出最佳组件定位的精确建议。
