Vertical Extension of the T-Capsulotomy Incision in Hip Arthroscopic Surgery Does Not Affect the Force Required for Hip Distraction: Effect of Capsulotomy Size, Type, and Subsequent Repair

Abstract

Background: Interportal and T-capsulotomies are popular techniques for exposing femoroacetabular impingement deformities. The difference between techniques with regard to the force required to distract the hip is currently unknown. Purpose: To quantify how increasing interportal capsulotomy size, conversion to T-capsulotomy, and subsequent repair affect the force required to distract the hip. Study Design: Controlled laboratory study. Methods: Eight fresh-frozen cadaveric hip specimens were dissected and fixed in a materials testing system, such that pure axial distraction of the iliofemoral ligament could be achieved. The primary outcome measure was the load required to distract the hip to a distance of 6 mm at a rate of 0.5 mm/s. Each hip was tested in the intact state and then sequentially under varying capsulotomy conditions: 2-cm interportal, 4-cm interportal, half-T (4-cm interportal and 2-cm T-capsulotomy), and full-T (4-cm interportal and 4-cm T-capsulotomy). After serial testing, isolated T-limb repair and then subsequent complete repair were performed. Repaired specimens underwent distraction testing as previously stated to assess the ability to restore hip stability to the native profile. Distraction force as well as the relative distraction force (percentage normalized to the intact capsule) were compared between all capsulotomy and repair conditions. Results: Increasing interportal capsulotomy size from 2 to 4 cm resulted in significantly less force required to distract the hip (P < .001). The largest relative decrease in force was seen between the intact state (274.6 ± 71.2 N; 100%) and 2-cm interportal (209.7 ± 73.2 N; 76.4% ± 15.6%; P = .0008). There was no significant mean difference in distraction force when 4-cm interportal (160.4 ± 79.8 N) was converted to half-T (140.7 ± 73.5 N; P = .270) and then full-T (112.0 ± 70.2 N; P = .204). When compared with the intact state, isolated T-limb repair partially restored stability (177.3 ± 86.3 N; 63.5% ± 19.8%; P < .0001), while complete repair exceeded native values (331.7 ± 103.7 N; 122.7% ± 15.1%; P = .0008). Conclusion: The conversion of interportal capsulotomy to T-capsulotomy did not significantly affect the force required to distract the hip in a cadaveric model. However, larger interportal capsulotomies resulted in significant stepwise decreases in distraction force. When performing interportal or T-capsulotomy, the iliofemoral ligament strength is significantly decreased, but complete capsular repair demonstrated the ability to restore joint stability to the native, intact hip. Clinical Relevance: Increasing interportal capsulotomy size decreases the force required to distract the hip. In an effort to maximize visualization and minimize the magnitude of iliofemoral ligament fibers cut, many surgeons have moved from extended interportal capsulotomy to T-capsulotomy. Interportal and T-capsulotomies result in equivalent hip distraction, partial capsular repair marginally improves hip stability, and only complete repair has the ability to restore the hip to its native biomechanical profile.