To the Editor,
I read the article by Stirling et al. with great interest [3]. Although the current evidence on the effect of hip center location on the functional outcomes of THA is limited, the authors provided a good review of the available data. Stirling et al. even cited two of my team’s studies [1, 2]. I wanted to make a contribution rather than a criticism to prevent any misunderstanding by readers regarding our studies.
The authors emphasized that my team’s studies [1, 2] had selection bias, which is theoretically true since we only included patients with good functional outcomes and without any complications. However, as we also stated in our articles, our studies aimed to analyze the differences in walking characteristics solely as a function of the hip center’s location. That’s why we sought to minimize between-group differences through tight inclusion and exclusion criteria in terms of other parameters that might influence walking pattern. Specifically, we required all patients in both groups to have had comparably severe DDH prior to surgery, as well as excellent Harris Hip Scores, reasonably similar limb lengths, and complete intermediate-term follow-up after surgery. By doing so, we attempted to build an in vivo biomechanical setting analyzing the biomechanical effects of hip center location rather than a comparison of functional outcomes. Although we believe that the authors were aware of our study methods, we wanted to make it clear for any readers who may draw conclusions from the paper by Stirling et al [3].
Indeed, it would not be appropriate for readers to conclude from my group’s articles [1, 2] that both high and anatomical hip center techniques provide similar functional outcomes, since the study design does not allow such a conclusion. Rather, my team wanted to compare those techniques biomechanically by gait analysis to see whether high hip center has any adverse effects on gait parameters. Although unilateral high hip center affected some gait parameters adversely, it is not possible to foresee whether those differences will transform into anything noteworthy in longer-term follow-up studies.
Footnotes
(RE: Stirling P, Viamont-Guerra M-R, Strom L, et al. Does cup position at the high hip center or anatomic hip center in THA for developmental dysplasia of the hip result in better Harris hip scores and revision incidence? A systematic review. Clin Orthop Relat Res. 2021;479:1119-1130.)
The author certifies that there are no funding or commercial associations (consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article related to the author or any immediate family members.
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.
The opinions expressed are those of the writer, and do not reflect the opinion or policy of CORR® or The Association of Bone and Joint Surgeons®.
References
- 1.Karaismailoglu B, Erdogan F, Kaynak G. High hip center reduces the dynamic hip range of motion and increases the hip load: a gait analysis study in hip arthroplasty patients with unilateral developmental dysplasia. J Arthroplasty. 2019;34:1267-1272. [DOI] [PubMed] [Google Scholar]
- 2.Karaismailoglu B, Kaynak G, Can A, Ozsahin MK, Erdogan F. Bilateral high hip center provides gait parameters similar to anatomical reconstruction: a gait analysis study in hip replacement patients with bilateral developmental dysplasia. J Arthroplasty. 2019;34:3099-3105. [DOI] [PubMed] [Google Scholar]
- 3.Stirling P, Viamont-Guerra M-R, Strom L, et al. Does cup position at the high hip center or anatomic hip center in THA for developmental dysplasia of the hip result in better Harris hip scores and revision incidence? A systematic review. Clin Orthop Relat Res. 2021;479:1119-1130. [DOI] [PMC free article] [PubMed] [Google Scholar]