The Incidence of Dislocation (Utilizing a Neck Sparing Stem) in Community Based Practices with the Posterior Approach

Purpose. To evaluate early and mid-term risk factors and dislocation rates in the posterior surgical approach in three separate community private practices using a short curved neck-sparing total hip stem design. Material and Methods. The three senior authors performed 338 short curved neck-sparing stem designs since April 2010 to June 2014.  Various cementless acetabular components were used for all three surgical centers based on preoperative and intraoperative risk factors. All cases were reviewed retrospectively for incidence of dislocation after surgery. Version and inclination of the acetabular component and version of the femoral component were assed intra-operatively prior to final implantation. Various risk factors were reviewed including surgical approach, cup position, combined cup and stem positioning, and femoral head size. There have been significant papers in the past ten years that have recommended large head diameters to reduce the chances of head/neck mechanical impingement. Since the neck-sparing designs have a potentially increased risk of mechanical impingement head diameters were restricted to 32 mm or larger. In the smaller patient profile if a 32 mm head size could not be reached a dual-mobility style implant was chosen or stem choice was changed to a conventional style design. Results. Historically the posterior approach has had higher reports of dislocations as compared to direct anterior, anterolateral or straight lateral approach in conventional cemented and cementless implant designs. Older neck-sparing designs of conventional stem length by Freeman, Townley and Whiteside have not reported any increased dislocation problems but these stems have been associated with modified acetabular component designs, including the short curved neck sparing design of Pipino back in the 1980s. Incidence of dislocation in our series utilizing a short curved neck-sparing stem with more traditional hemispherical cementless acetabular components was 3 or 0.88%. Conclusion. Neck sparing stem designs do save significantly more bone and require less soft tissue dissection as compared to conventional cementless stem designs. Mechanical risk factors are increased with the use of short curved neck-sparing stem designs. Careful pre-operative and intra-operative evaluation does reduce the risk factors resulting in low and in some cases lower than previous published rates with conventional style stems. Short curved neck sparing stems do provide safe and reliable reproduction of the joint mechanics in routine primary total hip arthroplasty in both short and mid term results. Key Words: hip, arthroplasty, posterior approach, dislocation, neck sparing, and risk factors