Authors: Austin E. Wininger, Matthew J. Kraeutler, Haley Goble, Justin Cho, Omer Mei-Dan, Joshua D. Harris
Categories: Technical Note
Source: Arthroscopy Techniques
Hip arthroscopy is commonly performed to treat femoroacetabular impingement syndrome. A post-assisted arthroscopic hip preservation surgery approach provides joint distraction for central-compartment access. Owing to the location, compression of the post in the perineum may cause injuries to the pudendal nerve, perineal soft tissue, or genitourinary system. A postless technique significantly reduces the risk of these complications. Postless arthroscopy uses friction between the patient’s torso and the table surface to permit distraction without the post. An air arthrogram, general anesthesia with muscle paralysis, and variable degrees of Trendelenburg positioning reduce the force needed for joint distraction. Early postless literature suggested Trendelenburg angles of approximately 15°, which may be disorienting to surgeons and compromise the precision and accuracy of the surgical procedure. With the described technique, hip arthroscopy can be effectively performed with a Trendelenburg angle of less than 5° in nearly every case. Understanding the physics of postless hip arthroscopy using free-body diagrams of inclined planes with friction permits surgeons to understand the required Trendelenburg angle of the bed, the force of traction for any patient given his or her body habitus, and the coefficient of static friction of the table surface to achieve a minimum amount of joint distraction.
Arthroscopic hip preservation surgery plays an important role in the management of femoroacetabular impingement syndrome via cam and pincer morphology correction and labral preservation. This results in improvements in the health of the hip articular cartilage, subchondral bone, and synovial fluid–joint homeostasis milieu.^1^^,^^2^ Traction is required to treat central-compartment pathology during hip arthroscopy. Hip joint distraction, in and of itself, has inherent risks of complications.^3^ Postless hip arthroscopy is a meaningful innovation that reduces the risk of perineal complications (pudendal nerve pathology and compression-related genitourinary and gynecologic soft-tissue injuries) that can be observed after post-assisted surgery.4, 5, 6 A postless technique may even enable a quicker recovery time with a shorter time from surgery to hospital discharge without affecting venous blood flow or nerve function in the operative leg.^7^^,^^8^
Postless distraction avoids the need to apply countertraction to the nonoperative leg and relies on friction between the patient and the bed (achieved through a soft high coefficient-of-friction pad) to counter the traction needed to distract the hip joint.^9^ Use of an air arthrogram may disrupt the labral suction seal and reduce the traction force required to achieve adequate distraction.^10^ Trendelenburg positioning adds gravitational force for further countertraction and reduction in the traction force necessary to achieve safe joint access for visualization and instrumentation. Early postless hip arthroscopy literature suggested Trendelenburg positioning upwards of 15°.^8^^,^11, 12, 13 This amount of bed tilt can be disorienting to the surgeon and present technical challenges to skillful execution of the procedure. We present a safe and effective technique for postless hip arthroscopy, defining all of the physical variables involved for optimal hip joint distraction.
General anesthesia with muscle paralysis is used in all cases, without regional or neuraxial anesthesia. The patient is positioned supine on a specialized post-free hip distraction system (Pivot Guardian Distraction System; Stryker, Greenwood Village, CO) (Fig 1). On the surface of the bed is a high-friction, soft and compressible foam pad that provides friction against the dorsum of the patient’s body while pulling axial distraction on the operative limb. This friction is the inherent component necessary to achieve postless distraction. The nonoperative lower extremity is placed in approximately 20° of abduction, 5° of flexion, and neutral rotation. A gentle longitudinal pull of axial distraction is applied to the nonoperative lower extremity and released to ensure there is no excessive slack or force anywhere in the extremity. The operative extremity is placed in approximately 0° of abduction, 0° of flexion, and variable degrees of rotation dialed to approximate a perpendicular neck on an anteroposterior radiograph based on the patient’s femoral version. Before any longitudinal traction is pulled, a 17-gauge 6-in spinal needle is used to enter the hip joint anterolaterally through the trajectory of the anterolateral portal, aiming for the proximal femur just above the zona orbicularis but distal to the labrum. Fluoroscopy confirms the intra-articular position. A 30-mL sterile syringe is used to perform an air arthrogram to provide positive pressure and to attempt to break the labral negative suction seal with 10 to 20 mL of air (Fig 2).^10^^,^^14^ Live low-dose and low–pulse rate continuous fluoroscopy can visualize femoral head translation with increasing the volume of air injected (Video 1).^15^^,^^16^ Femoral head translation likely represents a patient’s symptoms of instability (or microinstability). The desired magnitude of joint distraction is typically a minimum of 10 to 12 mm on an anteroposterior fluoroscopic image at the location of joint entry (approximately 30–clock face position to 1-o’clock position on an acetabular clock face). The Trendelenburg angle of the bed can be adjusted pending the ease of distraction. Precise joint distraction is measured by pushing a radiopaque calibration ball (diameter, 25.4 mm) as a magnification marker against the patient in the soft spot between the anterosuperior iliac spine and the greater trochanter to place the ball into the fluoroscopy field in the coronal plane of the hip joint (Fig 3). The traction force applied and the Trendelenburg angle are measured and recorded (Fig 4). The force of distraction is the minimum force (pound-force or Newtons) necessary to achieve the desired distraction distance—but no more than that force. Although increased Trendelenburg positioning may increase distraction, less than 5° (and frequently <2°) can be used in most, if not all, hip arthroscopy procedures. High degrees (>5°-10°) of Trendelenburg positioning may lead to surgeon disorientation, portal trajectory errors, and suture anchor placement challenges, among other technical difficulties, owing to the relative pelvic tilt during the procedure. After the joint is entered and the interportal capsulotomy created, the distraction force is again measured and recorded. Once the central-compartment work is completed, the traction time is recorded. After the central-compartment work, off-traction work in the peripheral, peritrochanteric, and deep gluteal compartments is performed as needed. Capsular closure is performed in all cases.
Fig 1 Final patient positioning using Pivot Guardian Distraction System for postless hip distraction. The patient is in the supine position for arthroscopy on the right hip (asterisk) with the bed at a Trendelenburg angle of less than 5°. The C-arm is brought in from the contralateral side.
Fig 2 Intraoperative fluoroscopic image showing use of 17-gauge spinal needle to penetrate hip joint anteriorly and inject 10 to 20 mL of air to perform air arthrogram and break labral suction seal. The asterisk indicates the right hip joint.
Fig 3 A radiopaque calibration ball (diameter, 25.4 mm) is placed into the fluoroscopic field of view to measure precise joint distraction just prior to starting hip arthroscopy. The asterisk indicates the left hip joint, and the arrow indicates appropriate joint distraction of 10 to 12 mm.
Fig 4 Use of Pivot Guardian Distraction System to measure Trendelenburg angle of bed (5°) with inclinometer (asterisk, left) and force of distraction (roughly 55 lb) with traction force gauge (pound sign, right).
Understanding the physics of free-body diagrams of inclined planes with friction permits hip arthroscopy surgeons to manipulate any modifiable variable in the surgical field setup (Fig 5). The proportional impact of each variable can be determined with basic physics equations. The Trendelenburg position needed (in degrees) is a modifiable variable, with increasing degrees needed for hips more resistant to distraction. The force necessary to break the labral suction seal can be significantly reduced with an air arthrogram. The force necessary to gain further distraction on joint entry can be significantly reduced with an interportal capsulotomy. The patient’s body weight is an unmodifiable variable with counterintuitive findings for distraction. With a post-assisted approach, distraction is usually easier in lighter patients. Using a postless approach requires the patient’s body weight to compress the pad and engage the friction of its surface, permitting distraction. Distraction is typically more challenging in lighter patients. Conversely, distraction may be easier in heavier patients. The effect of complete neuromuscular blockade and muscle relaxation (zero twitches on train-of-4 testing) cannot be emphasized enough. This modifiable variable requires communication and coordination with the anesthesia team. The bed’s surface is usually covered with a disposable pad with a high coefficient of static friction (Fig 6). This modifiable variable can be calculated if all other variables in the equation are known. Typically, the companies that produce the proprietary pads used in postless hip arthroscopy do not make the coefficient of static friction publicly known. Once a specific pad’s coefficient is known, it can then be used as an independent variable to calculate other unknowns in the free-body diagram’s equations.
Fig 5 Free-body diagram showing forces involved in achieving postless hip joint distraction during supine right hip arthroscopy. (F
FR, force of friction; FG, force of gravity; FN, normal force; F~⟂, perpendicular force; F∥, parallel force; FLabrum~, force necessary to disrupt the labral suction seal; F~Capsule~, force necessary to stretch the capsule.)
Fig 6 Examples of foam pads with high coefficients of static friction that can be placed between patient and bed. The pads are not specific to one manufacturer.
Safety is a primary concern with the introduction and adoption of any technology. Without a perineal post blocking the patient from falling off the bed toward the feet, the patient must be positioned proximal enough on the bed so that distraction does not pull the patient off the bed. Bed extensions can obviate this concern (Fig 7). If the postless bed used does not permit a bed extension, then the cognizant surgeon must ensure patient safety and avoid this potentially catastrophic complication. However, most hip arthroscopy beds have metallic bases that may preclude the fluoroscopic unit base to have sufficient room under the bed if the patient is too proximal on the bed. Given the friction mechanism with the patient’s dorsal surface skin and the effect of longitudinal skeletal distraction on the pelvis, variable degrees of anterior pelvic tilt predictably occur (Fig 8). This may affect labral anchor placement, requiring the surgeon to either have a further distal starting point on the skin if using a straight guide or use a curved guide to avoid articular penetration.
Fig 7 Postless hip arthroscopy setup using bed extension. It should be noted that adequate femoral head distraction was achieved during this case with a 0° Trendelenburg angle of the bed. The asterisk indicates the right hip, and the pound sign indicates the bed extension in place. The black arrow on the fluoroscopic image indicates adequate hip joint distraction. The blue arrow points to a magnified view of the force gauge.
Fig 8 Patient positioning for postless distraction of right hip (asterisk) during supine hip arthroscopy with pink pad positioning device. Patients who weigh less may require greater degrees of Trendelenburg positioning of the bed to achieve distraction. The dashed blue line indicates hyperextension of the lumbar spine.
Most arthroscopic hip preservation surgery literature reports the use of a perineal post. Although most pudendal neurapraxia cases and perineal soft-tissue injuries after hip arthroscopy are transient, a small, albeit nonzero, percentage are permanent. A recent systematic review indicated that the incidence of post-related complications may be under-reported in the literature and found that there is a 5 times greater incidence of these complications in the prospective versus retrospective hip arthroscopy literature.^6^ A major benefit of postless distraction systems is the absence of perineal compression with a lower traction force required to safely distract the hip joint.^17^
A postless technique may be a significant innovation in the field of arthroscopic hip preservation surgery because it can safely and effectively eliminate groin-related complications (Table 1).^18^^,^^19^ As with all aspects of a technical field such as surgery, “technology is something you buy and technique is something you master” (F. Matsen, M.D., written communication, October 2023). Thus, skillful application of traction with a post-assisted approach also has the potential to have a low perineal soft-tissue and pudendal nerve complication incidence. In more than 20 years and over 7,000 hip arthroscopy procedures, Larson^20^ has had zero known pudendal nerve injuries or cases of perineal skin breakdown. This is because of skillful lateralizing the perineal post over the medial thigh rather than over the medial ischial tuberosity, using Trendelenburg positioning to decrease force in the perineum, performing an air arthrogram breaking the labral suction seal prior to pulling distraction, and minimizing traction force and traction time. That being said, a recent cadaveric study revealed a significant pressure increase with an increase in traction force at the ischial tuberosity and genital region, suggesting that pudendal nerve injury may be due to a compression force rather than a tensile traction force.^21^ By eliminating the perineal post, surgeons do not have to worry about compression-related groin injuries. Given the significant learning curve of hip arthroscopy, adopting a postless technique may enable teaching faculty and surgeons in their learning curve to operate with less stress if the traction time is unburdened by the worry of post-related perineal or pudendal nerve complications.
The authors report the following potential conflicts of interest or sources of M.J.K. is on the Arthroscopy editorial or governing board. J.C. is on the Arthroscopy editorial or governing board. O.M-D. receives royalties or licenses from Stryker and owns stock or stock options in HeapSi and MITA. J.D.H. receives royalties or licenses from SLACK and Thieme Medical Publishers; receives consulting fees from Smith & Nephew; has a leadership or fiduciary role in American Academy of Orthopaedic Surgeons, Arthroscopy, American Orthopaedic Society for Sports Medicine, International Society of Arthroscopy, Knee Surgery, and Orthopaedic Sports Medicine, Arthroscopy Association of North America, and Orthopaedic Research Society; and owns stock or stock options in PatientPop. All other authors (A.E.W., H.G.) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Full ICMJE author disclosure forms are available for this article online, as supplementary material.