CORR Insights®: Prominent Anterior Inferior Iliac Spine Morphologies Are Common in Patients with Acetabular Dysplasia Undergoing Periacetabular Osteotomy

Where Are We Now?

Acetabular reorientation osteotomies are commonly used for treating patients with symptomatic dysplasia. While the Bernese periacetabular osteotomy (PAO) and similar variants are extraarticular and preserve the mechanical integrity of the pelvic posterior column, spherical or dial osteotomies often result in the violation of the most-distal portion of the acetabulum, and double or triple osteotomies cut through the ischium and ilium [1]. Preservation of the articular surfaces and mechanical stability are two key advantages of joint-preserving modern osteotomies like PAOs, but these are difficult operations to do. One of the most challenging steps is to judge the appropriate correction of acetabular deformity. There is a fine line between excess correction (resulting in intra- or extraarticular mechanical impingement) and not enough correction (with insufficient coverage of the femoral head) [3]. A prominent anterior inferior iliac spine (AIIS) can potentially cause extraarticular impingement in dysplastic hips managed with acetabular osteotomy reorientation.

In this CT imaging–based paper, Nestorovski et al. [4] found that the morphology of the AIIS could potentially cause impingement in 72% (36 of 50) of patients undergoing Bernese PAO for symptomatic residual dysplasia. In light of this finding, I believe surgeons should focus on the shape and size of the AIIS while evaluating the most appropriate correction of acetabular deformities.

Where Do We Need To Go?

Certainly, we still need to better understand the extent and clinical relevance of subspinous impingement in dysplastic hips. We know that in nondysplastic hip joints with extraarticular impingement, prominent AIIS and the anterior portion of the femoral neck cause restriction of ROM in flexion and internal rotation, and can cause groin pain. Similarly, in reconstructive surgery, depending on the extent of correction required to achieve sufficient femoral head coverage, the AIIS may be moved so far anteriorly and laterally that it may cause extra-articular contact against the proximal femur. This leads to two important questions: (1) what is the magnitude of clinically relevant AIIS prominent morphology, and (2) what can we do to identify it early, manage it appropriately, and prevent likely impingement?

How Do We Get There?

Let’s start considering the first question: Restriction of hip motion in flexion and internal rotation can be clinically relevant in the presence of subspinous extraarticular impingement. Finite element analysis (FEA) and ROM computational simulation of common dysplastic hip models with different AIIS shapes can help identify at-risk morphologies [5]. These simulations could be performed using the Type 3 classification of AIIS morphology proposed in the present study.

Regarding the second question and how to tackle early identification and surgical management of prominent AIIS, awareness of the condition and CT (preferably associated with FEA) are essential for adequate preoperative planning [3, 6].

A prospective analysis of patients with symptomatic hip dysplasia presenting with prominent AIIS morphology would give us a better understanding of the clinical importance of subspinous conflict. The coordinated participation of high-volume institutions will also help confirm—with a larger sample size—the findings of the current study, which suggested that there is no association between the severity of acetabular dysplasia and morphology of the AIIS. The International Hip Society, with its numerous joint-preserving surgery members, could be a potential platform to get this project off the ground. I would refrain from considering a randomized clinical trial because of the associated high costs and for ethical limitations—would it be appropriate to allocate in the no-intervention cohort a Type 3 AIIS patient with impingement signs and restricted hip flexion at surgery?

The surgical management of a prominent AIIS causing impingement against the proximal femur after acetabular reorientation should not be a challenge. Current soft tissue—sparing surgical approaches for juxta-articular osteotomies usually preserve the origin of the direct head of the rectus femoris over the AIIS [2]. However, in the presence of a subspinous impingement, the surgeon could use the modified Smith-Petersen approach described originally for the Bernese procedure, which included the release of the tendon, and therefore carry out a safe reshaping/decompression of the AIIS. The rectus tendon could then be reattached to the pelvis with a stable transosseous suture. Incidentally, the Smith-Petersen approach was (and still is) a common surgical procedure used for full exposure of the anterior iliac spine region.

A prominent morphology of the AIIS can be identified by the expert eye. I would not be surprised if the pioneers of hip osteotomies would handle a prominent spine abutting over the joint area as part of their normal approach by reshaping it to more-closely resemble normal anatomy, perhaps without even mentioning it in the texts they wrote. As Michelangelo was to sculpture, so were the old masters of osteotomy to orthopaedic surgery.