Arthroscopic Iliopsoas Release: Letter to the Editor

Dear Editor:

We congratulate the authors on their excellent work in the article titled “The Functional and Structural Outcomes of Arthroscopic Iliopsoas Release” by Brandenburg et al. ¹ In this study, patients who had undergone hip arthroscopic surgery at least 1 year prior were considered. Eighteen of 71 patients who underwent endoscopic iliopsoas release for symptomatic snapping along with the arthroscopic management of chondrolabral abnormalities (release group) were compared to 18 of 54 patients undergoing treatment for femoroacetabular impingement (FAI; control group). Patients were then invited by mail to undergo magnetic resonance imaging (MRI) and strength testing. They found that patients in the release group had muscle atrophy confirmed by 25% volume loss on MRI and a decrease of seated hip flexion strength of 19%. They recommended that surgeons employ a high threshold before considering this procedure during the comprehensive management of FAI. We commend the authors on this potentially important finding because loss of hip flexion strength would be an undesirable side effect of an otherwise historically satisfying procedure.^3,4,6 With this in mind, there are some limitations in the methodology and implications, which highlight some areas of need for further study.

Firstly, there may be significant selection bias, which could skew the results. Of 71 patients available for inclusion, only 18 agreed to undergo MRI and strength testing. Patients with problems or negative symptoms after surgery might be more inclined to undergo another examination, while patients who were satisfied with their outcomes might be less likely to participate. This bias in patient selection may incorrectly suggest a potential for poorer clinical outcomes. This may also bias the results of strength testing; patients who are more symptomatic would potentially have more muscle atrophy and lesser flexion strength, which in turn may negatively influence the results, even when comparing to the contralateral side. Furthermore, the authors do not indicate how the control group was selected, and it does not appear to comprise a consecutive set of surgical procedures. This introduces additional potential selection bias in the control group. Indeed, if imaging were performed only on the patients within the control group who had negative outcomes, they might show similar weakness and atrophy.

Eligibility for inclusion of interested participants was reviewed by telephone. Hammarstedt et al ⁵ showed that telephone interviews of patients can lead to altered patient responses in regards to questions regarding outcomes as compared to email or in-person interviews, which could be a confounding variable. Therefore, this too may introduce an element of response bias.

A randomized controlled study of patients with internal snapping who underwent iliopsoas fractional lengthening compared to those without internal snapping, while still addressing intra-articular abnormalities, may be a more appropriate way to study this topic. However, because this may not be technically feasible, prospectively collected data with greater than 80% patient follow-up might reduce the effect of selection bias. Such a study might involve matched cohorts of consecutive surgical procedures, performed during a defined study period by the same surgeon(s), allowing an “apples-to-apples” comparison.

A number of studies, describing both open and endoscopic iliopsoas fractional lengthening, have shown this procedure to be safe and effective, either in isolation or during the treatment of coexisting intra-articular abnormalities. Dobbs et al ² studied 9 adolescent patients (11 hips) who underwent open iliopsoas fractional lengthening for internal snapping via a modified iliofemoral approach, all but one of whom were involved in competitive sporting activity before surgery. At an average follow-up of 4 years, they found that all of the patients were able to return to their preoperative level of activity without subjective or objective weakness of hip flexion strength. Although the patients in that study did not undergo strength testing by a dynamometer, it suggests that no appreciable loss of function during sporting activity was noted by active patients, who all reported satisfaction with the outcomes of the procedure. ² It has become clear from recent studies that internal snapping may not only be a part of a constellation of abnormalities but may itself be the cause of labral injuries. Domb et al ³ reported on 25 patients who underwent isolated iliopsoas fractional lengthening for internal snapping and iliopsoas impingement, which was identified to be the cause of labral injuries seen at arthroscopic surgery. At a mean follow-up of 21 months, the patients had significant improvement in all patient-reported outcome scores and were satisfied with the outcomes of the procedure. ³

Patients undergoing arthroscopic surgery for painful snapping and concurrent intra-articular hip abnormalities also appear to do better when the snapping resolves than when it persists. El Bitar et al ⁴ reported on 55 patients with intra-articular hip abnormalities who underwent arthroscopic iliopsoas release as part of their arthroscopic management. At a minimum of 2-year follow-up, 81.8% had a resolution of snapping. The patients whose snapping resolved reported excellent satisfaction (≥7/10) with the procedure and had significantly greater improvement in 4 different patient outcome scores than patients with persistent snapping. Of the 25 patients in that study who completed perioperative questionnaires, 10 reported their physical ability as much improved, 12 as improved, and 1 as no change. Two patients did not fill out the questionnaire. ⁴

Lastly, even with complete tendon release at the level of the lesser trochanter, which potentially results in greater muscle weakness than partial (fractional) lengthening performed more proximally, good outcomes have been reported. Ilizaliturri et al, ⁶ in a prospective outcome study on patients who underwent endoscopic iliopsoas release at the level of the lesser trochanter versus those who underwent iliopsoas release from the peripheral compartment, found equally favorable Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores at final follow-up.

These studies and others suggest that given the correct indication (ie, painful internal snapping), iliopsoas release is both safe and effective, either in isolation or as part of the comprehensive management of intra-articular abnormalities. We commend the authors for bringing up strength loss and atrophy as important areas for future study. Furthermore, the authors employed an elegant imaging methodology to measure the volume of the iliopsoas and a useful strength measurement apparatus, both of which may prove useful in future studies. The current study is limited by a low percentage of follow-up and significant potential for selection bias and response bias. Because of these limitations, no conclusions can or should be made regarding efficacy, clinical outcomes, or adverse effects. Future studies that include a rigorous study design, consecutive matched or randomized cohorts, and a high rate of clinical follow-up may enable us to better assess the usefulness, and the risks, of iliopsoas lengthening.