CORR Insights®: No Clinically Important Differences in Thigh Pain or Bone Loss Between Short Stems and Conventional-length Stems in THA: A Randomized Clinical Trial

The study by Won et al. [⁹] addresses a concerning complication after THA, namely thigh pain in conjunction with a cementless femoral stem. In their prospective, randomized study, 100 patients were randomized to receive either a short-length or standard-length, titanium, flat, tapered stem from the same manufacturer (Zimmer Biomet, Warsaw, IN, USA). Thigh pain was evaluated with a 10-point VAS scale, and bone mineral density was assessed with dual-energy x-ray absorptiometry (DEXA) scans. At a minimum of 5 years of follow-up, the authors could detect no difference in thigh pain, Harris hip scores, or loosening between the two groups, while the DEXA scans showed a slightly smaller decrease in bone density in Gruen Zones 2, 3, and 5 in the shorter-stem group.

Thigh pain after THA can result in impairment and patient dissatisfaction. The incidence and etiology of stem-related thigh pain has remained somewhat elusive over a generation, and while many researchers have implicated design features such as stem material [^{2, 7}], stem size [⁸], stem shape [⁶], and extent of porous coating [⁵], I’m not aware of any high-quality studies that have answered these questions. It seems that the challenges of stem fixation and durability have been solved, with published high survivorship rates across many stem designs. Despite excellent survivorship, manufacturers continue to develop new designs to address the practical challenges that surgeons face. Over time, stems have gradually become shorter to facilitate implantation and avoid the implantation of diaphyseal bone, and stems have been designed with reduced shoulders to spare trochanteric bone and facilitate implantation with muscle-sparing approaches. Additionally, some stems now use different types and extents of coating. Once thought to be a design taboo, collars have been added to certain tapered cementless stems to enhance early stability [^{3, 4}]. Although this evolution in design may appeal to surgeons, any design change may have unexpected consequences on other metrics such as rates of fixation, periprosthetic fracture, and patient-reported thigh pain. Furthermore, most new implant designs come with an additional cost, so a higher cost combined with the possibility of deterioration in outcomes makes the development of new designs somewhat perilous.

One example is illustrated in a study by Amendola et al. [¹]. This study reported a single surgeon’s experience with a new, shorter, titanium tapered stem. Although ingrowth was excellent in their 261 hips, 16% of patients reported mild thigh pain, 9% reported moderate-to-severe pain, and one patient underwent revisions for severe thigh pain. Because of these results, the senior author abandoned the use of the product. Unfortunately, it remains unclear why the stem in that study had this unfortunate outcome. Curiously, the design of this stem resembles many similar products on the market that have lower published rates of thigh pain [^{6, 9}]. This illustrates one current conundrum—researchers haven’t reliably pinpointed the factors that contribute to stem-related thigh pain in the presence of an aseptic, well-fixed stem.

This well-done Level I study by Won et al. [⁹] has addressed one specific question related to one specific product regarding stem-related thigh pain: does a shorter version of the same stem reduce (or increase) the rate of patient-reported thigh pain? The answer shown from the results of this study was convincingly no, with several other metrics also demonstrating no difference in outcomes between the shorter and longer stems. Interestingly, despite identical results, the authors recommended in their conclusion that the longer stem be used because of its longer track record. Some, like myself, may have come to the opposite conclusion: that with identical 5-year outcomes, either stem could be used, and preference may be given to the shorter version for ease of insertion and bone preservation.