Should we be concerned when the anterior approach to the hip goes accidentally medial? A retrospective study.

Background: The direct anterior approach is increasingly used for primary total hip arthroplasty (THA) due to its minimally invasive nature and rapid recovery time. Difficulties in identifying the correct intermuscular interval can arise during the procedure, sometimes resulting in excessive medial exposure. This study aimed to evaluate demographics and risk factors, outcomes, and potential complications in those THA patients in which a medialized approach was performed.

Methods: We retrospectively reviewed cases of anterior THA to identify cases where the surgical approach to the hip was more medial than the standard interval. Demographic data, operative time, blood loss, intraoperative and postoperative complications, radiographic findings were collected and compared with a control group of 50 THA performed using the standard anterior intermuscular interval.

Results: In a series of 1,450 anterior total hip arthroplasty (THA) procedures performed between January 2018 and December 2021, with an average follow-up of 33 ± 22.3 months, six patients (0.4%) had a medialized surgical interval. In one case the superficial layer was medial to the sartorious muscle while in the other five cases, the interval was lateral to the sartorius superficially, and medial to the rectus femoris deeply. Four out of 6 patients (66.6%) showed neuropraxia affecting the femoral nerve, and 3 out of 6 (50%) had involvement of the lateral femoral cutaneous nerve. In 6 out of 6 patients (100%), surgery was performed during the learning curve of DAA. No patients in the control group developed femoral nerve neuropraxia, and 2 out of 50 patients (4%) showed involvement of the lateral femoral cutaneous nerve.

Discussion and conclusion: The anterior approach can rarely result in excessive medial exposure to the hip joint, especially during the learning curve. In our study cohort, an increased rate of neurological complications and reduced outcomes were observed, thereby rendering this event of particular clinical significance. To avoid unconventional intermuscular intervals, patient positioning and correct identification of the muscle bellies by recognizing the orientation of the muscle fibers are useful, together with the identification and ligation of the circumflex vessels, to ensure the identification of the correct intermuscular interval.