Biomechanical Effect of Capsular Shift in the Treatment of Hip Microinstability. Creation and Testing of a Novel Hip Instability Model

Abstract

Objectives:The objective of the study was to create a cadaveric model of hip capsule laxity and evaluate the biomechanical effects of a capsular shift used to treat hip instability on this model.Methods:Eight fresh frozen cadaveric hips, average age 58.5, were tested with a custom hip jig. To create the hip laxity model, the capsule was stretched in extension under 35Nm of torque for 1 hour in neutral rotation. Specimens went through a series of six testing conditions: intact, vented, stretched, capsulotomy, side to side repair, and capsular shift. Specimens were tested in internal (IR) and external (ER) rotational range of motion under 1.5 Nm of torque at 5 positions: 5° extension, 0°, 15°, 30° and 45° flexion. Maximum extension was measured at 5Nm torque, and femoral distraction under 40N and 80N of force. Following creation of the instability model, capsulotomy was performed just distal to and in line with the labrum from 12 o’clock to 4 o’clock through the entire substance of the iliofemoral ligament. Capsulotomies underwent two repairs, including a 1 cm capsular shift technique and side to side repair using #2 vicryl. Statistical analysis was performed using repeated measures ANOVA with TUKEY post-hoc analysis.Results:Analysis of the “stretched” state showed significantly increased IR at 5° ext, 0° flex, 15° flex, and 30° flex and increased distraction at 40N and 80N as compared to intact (Figure 1)(Table 1). Max extension increased by 6.6° between intact and stretched, however this was not statistically significant. Capsulotomy condition significantly increased ER and IR from intact at all flexion-extension positions. Furthermore, capsulotomy increased distraction at 40N and 80N, as well as max extension, as compared to intact. The repair restored IR back to the stretched state but not to the intact state at 5° ext and 0° flex (19.6° vs 24.5° and 21.8° vs 26.4°, respectively). The capsular shift significantly decreased IR compared to stretched state at 5° ext, 0°, and 15° flex, and at 5° ext and 0° compared to the vented state. Capsular shift restricted IR significantly more than repair at 5° ext, 0° flex, and 15° flex. Capsule shift and repair had similar effects on ER. Distraction distance at 40N and 80N was greater in the repair compared to the shift but this was not statistically significant. The capsular shift decreased distraction as compared to the stretched state but the repair did not. Maximum extension was significantly reduced back to the intact/vented state from the laxity state in the capsular shift but not in the repair.Conclusion:The instability model (stretched) was shown to have significantly greater range of motion, extension, and distraction than the intact condition. The greatest effects of capsular shift are seen with internal rotation, extension, and distraction with minimal effect on external rotation. The biomechanical effects of the capsular shift procedure in hip laxity patients show that its use can safely treat pathologic hip capsular laxity.

Repaired or unrepaired capsulotomy after hip arthroscopy: a systematic review and meta-analysis of comparative studies

“…6,7 Some authors have attributed postoperative instability to the violation of the capsule during the operation. 8,9 The fibrous hip joint capsule is a confluence of 4 ligaments (the iliofemoral, pubofemoral, and ischiofemoral ligaments and the zona orbicularis) that provides static Repaired or unrepaired capsulotomy after hip arthroscopy: a systematic review and meta-analysis of comparative studies constraint to the joint and is believed to be an important stabiliser of the hip joint. 10,11 During hip arthroscopy, a capsulotomy is necessary for visualisation and operation.…”

Hip Joint Capsular Anatomy, Mechanics, and Surgical Management

“…(For a detailed summary for each study's scope, methods, and observations, see Appendix Table I. ) in extension under 35 Nm of torque for 1 hour) and suggested that side-to-side repair only partially decreased distraction resistance, while a capsular shift approach restored joint stability 11 . Although capsular plication may help to restore joint stability in extreme cases of joint subluxation, it perhaps should not be a routine procedure for all capsular closures.…”

“…It is essential to understand that capsular characteristics and mechanical properties of the hip with pathological conditions are different (i.e., a thicker, stiffer capsule) than a healthy joint 38,50,52 ; thus, the need for full capsular closure may depend on several other confounding factors (e.g., age, sex, osseous anatomy, and muscle function) [53][54][55] . More importantly, since unrepaired capsulotomies have been shown to heal within 24 weeks postoperatively 56 , and completely resecting the iliofemoral ligament does not destabilize the native hip 43 , there is evidence that not all capsulotomies need to be repaired after The findings of in vitro cadaveric studies on the effects of capsular conditions and surgical stages, outlining the contributions of the interportal capsulotomy 5,7,8,10,11,14,46 and T-capsulotomy 6,11,14,15,46 and the effects of instability 7,[11][12][13]16,47 , effusion arthroscopy, especially when capsular contracture may be part of the pathological process. It is still unclear what leads to inherent or iatrogenic instability; thus, if the native head size is not substantially reduced or altered, capsular repair in the setting of a small arthroscopic capsulotomy may not be necessary in the otherwise congruent and stable hip 4,54,56 .…”

“…More importantly, how the hip capsule is managed during surgical interventions (preservation and arthroplasty) and its effects on joint function are increasingly recognized [5][6][7][8] . Several recent laboratory studies have provided new insights into functional mobility and stability of the hip joint that should be carefully considered during surgery [9][10][11][12][13][14][15][16][17][18][19][20] . The purpose of this review was to provide a comprehensive summary of the functional anatomy and material characteristics of the hip capsule and the effects of different capsular management techniques during arthroscopic and arthroplasty procedures on joint function.…”

Hip Capsular Management

“…When considering kinematic alterations to the hip joint, unrepaired interportal capsulotomy increases external rotation and decreases the force required for distraction as compared with the native hip. 15,[19][20][21] While interportal capsulotomy facilitates adequate visualization and access for diagnostic and interventional purposes, size of incision has been reported to correlate with the degree of iatrogenic instability. The length interportal capsulotomy may vary as small as 2 cm to greater than 6 cm depending on the pathology as well as surgeon preference.…”