Measurement of Hip Contact Pressure During Arthroscopic Femoroacetabular Impingement Surgery Mitsunori Kaya, M.D.
Abstract: Cam impingement is caused by jamming of an abnormal femoral head with an increased radius into the acetabulum during motion. Therefore, the elevation of the contact pressure during the motion is suspected to be an essential pathology of femoroacetabular impingement. However, there is no method to quantify the hip contact pressure during motion. The purpose of this Technical Note is to introduce a technique to measure the hip contact pressure during arthroscopic surgery. The author believes that the current technique will be a useful tool for the detailed investigation of the pathophysiology femoroacetabular impingement and thorough evaluation of its therapeutic signiﬁcance.
emoroacetabular impingement (FAI) is a mechanical conﬂict between the acetabulum and femoral head/neck.1 It has been proposed that this conﬂict leads to abnormal contact stresses within the physiological range of motion, resulting in degeneration of the cartilage/labrum of the acetabulum1 and the early onset of osteoarthritis in young patients.2 Cam impingement is caused by jamming of an abnormal femoral head with an increased radius into the acetabulum during forceful motion, especially ﬂexion.3 An aspherical femoral head contacts a spherical socket, thereby resulting in abnormally high pressures that drive cartilage damage in the anterosuperior acetabulum. The elevation of the contact pressure during motion is suspected to be an essential pathology of FAI.4 However, there is currently no method to quantify the hip contact pressure during motion. Herein, the author reports a technique to measure the hip contact pressure during arthroscopic surgery. The principle of this technique involves the measurement of pressure by using a ﬁberoptic microtransducer during arthroscopic FAI surgery. This technique enables quantitative determination of the hip contact pressure during forceful
From the Division of Orthopedic Surgery, Hitsujigaoka Hospital, Sapporo, Hokkaido, Japan. The author reports that he has no conﬂicts of interest in the authorship and publication of this article. Received September 17, 2016; accepted November 28, 2016. Address correspondence to Mitsunori Kaya, M.D., Hitsujigaoka Hospital, Aoba-Cho 3, Sapporo, Hokkaido 004-2211, Japan. E-mail: [email protected]
yahoo.co.jp Ó 2017 by the Arthroscopy Association of North America 2212-6287/16900/$36.00 http://dx.doi.org/10.1016/j.eats.2016.11.010
motion, providing a clue to the pathophysiology of FAI. In addition, it will lead to the establishment of qualitative methods to determine the proper area and depth that should be corrected during surgery.
Surgical Technique Accessing the Hip Joint Proper anesthesia with paralysis is required for safe distraction of the hip joint and prevention of complications during hip arthroscopy. The patient is placed supine on a traction table with all bony prominences well padded. Next, the operative leg is abducted and traction applied. It is then adducted to distract the
Fig 1. Arthroscopic image of a left hip viewed through the anterolateral portal. Traction is released and the hip ﬂexed approximately 90 to evaluate the peripheral compartment. Chondral damages are obvious in the distal anterior part of the femoral head (arrow).
Arthroscopy Techniques, Vol 6, No 3 (June), 2017: pp e525-e527
Table 1. Pearls and Pitfalls Pearls Transducer is inserted gently 1 cm proximal from the acetabular edge just below the anterior inferior iliac spine of the pelvis and pressures are recorded with the hip at 0 of ﬂexion with the neutral rotational position Hip is ﬂexed very slowly to 90 and measurements are taken when equilibrium is achieved Hip contact pressures are measured after the femoroplasty to evaluate the effect of the decompression of the deformities
Pitfalls Location of the tip of the transducer is critical for the reproducibility of the results
femoral head from the acetabulum. After routine preparation and draping of the hip, the procedure is begun by establishing standard anterolateral and midanterior portals to allow access to the central compartment. The capsule is cut with a beaver blade parallel to the labrum, connecting the anterior and anterolateral portals and extending medially as needed to address all intra-articular lesions. Routine diagnostic arthroscopy is performed to assess the ligamentum teres, cartilage surfaces, and labrum. The acetabular rim is lightly decorticated with a round burr to create a surface for the labrum to heal. To preserve as much labral tissue as possible, the labrum is not detached from the chondral junction. Labral repair is performed with a labral base reﬁxation technique or circumferential suture
Fig 2. Arthroscopic image of a left hip viewed through the anterolateral portal showing a transducer (arrow) that is inserted 1 cm proximal from the acetabular edge just below the anterior inferior iliac spine of the pelvis and pressures are recorded with the hip at 0 of ﬂexion in the neutral rotational position.
Fig 3. Arthroscopic image of a left hip viewed through the anterolateral portal. The hip is ﬂexed very slowly to 90 (arrow) and measurements are taken.
technique based on the labral thickness and quality of the tissue. All torn ﬁbers of the ligamentum teres are debrided with a shaver and electrocautery, leaving healthy, intact ﬁbers. Traction is then released and the hip ﬂexed approximately 90 to evaluate the peripheral compartment (Fig 1). Measurement of Intra-articular Hip Contact Pressure The intra-articular hip contact pressures are measured using a ﬁberoptic microtransducer (Camino intraparenchymal ﬁberoptic device; Camino Laboratories, San Diego, CA) and recorded on a strip-chart recorder (Table 1, Video 1).5 The 1.32-mm-diameter transducer
Fig 4. Arthroscopic image of a left hip viewed through the anterolateral portal. Femoroplasty (arrow) is performed and the contact pressures are measured. The hip is ﬂexed very slowly and measurements are taken with the hip at 0 of ﬂexion in the neutral rotational position to evaluate the effect of the decompression of the cam deformities.
HIP CONTACT PRESSURE DURING ARTHROSCOPIC SURGERY Table 2. Advantages and Limitations Advantages
The evaluation of hip contact pressure during the active motion is impossible
Quantitative method to measure the hip contact pressure investigating the pathophysiology of cam-type femoroacetabular impingement Conﬁrm the clinical signiﬁcance of the femoroplasty Intraoperative index of the proper area and depth of trimming
is inserted gently 1 cm proximal to the acetabular edge just below the anterior inferior iliac spine of the pelvis and pressures are recorded with the hip at 0 of ﬂexion in the neutral rotational position (Fig 2). Then the hip is ﬂexed very slowly to 90 and measurements are taken when equilibrium was achieved (Fig 3). The measurements are performed 3 times and the mean of the 3 trials is recorded. Once the measurement of the intraarticular hip contact pressure has been completed, the operative hip is ﬂexed up to 45 , and the osteoplasty of the cam-type deformity of the femoral head is performed. Intra-articular hip contact pressures are measured in the same manner to evaluate the effect of the decompression of the cam-type deformities on the hip contact pressure (Fig 4).
Discussion The technique described above provides a quantitative method to measure the hip contact pressure (Table 2). By using this method, the detailed investigation of the pathophysiology of cam-type FAI is possible. The author has observed by the preliminary investigations
that the contact pressures of the patients with cam-type FAI were elevated during hip ﬂexion. In contrast, the hip contact pressures of the patients with borderline dysplasia were not elevated, suggesting that the elevation of the contact pressure during motion might be a phenomenon peculiar to FAI. In addition, the author has also observed that the correction of cam-type deformity prevented the elevation of the hip contact pressure during forceful hip ﬂexion. These ﬁndings appear to conﬁrm the clinical signiﬁcance of femoroplasty for cam-type deformity. The author believes that the current technique will be applicable for the establishment of an intraoperative index for the proper area and depth of trimming. The visualization of physiological impingement between the acetabulum and femoral head/neck is practically impossible. This makes FAI very conceptual. For the detailed investigation of the pathophysiology of FAI and thorough evaluation of its therapeutic signiﬁcance, surgeons should continue to clarify the actual state of FAI. To do this in practice, the author believes that the current technique will be a useful tool.
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