Hip Instability

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CHAPTER 7 Hip Instability

Unlike the shoulder, which relies primarily on static and dynamic soft tissue restraints for its stability, the hip depends primarily on its osseous anatomy. The hip’s unique soft tissue envelope also plays a role in its stability, particularly when there is any significant deviation from normal.¹ When considering a patient with hip pain that is believed to be at least in some way the result of hip instability, both osseous and soft tissue constraints must be considered. Traumatic dislocation is typically accompanied by a history of an acute event. Atraumatic hip instability can result from repetitive rotational movements. The hypothesized mechanism for this type of instability is a subclinical capsular laxity accompanied by mild hip dysplasia that may progress over time.² Generalized laxity and connective tissue disorders are also causes of atraumatic instability.

Treatment of hip instability is largely based on the underlying cause. Diagnosing the cause of the problem begins with a proper history and physical examination, followed by plain radiography. Specialized radiography may be indicated, as well as further imaging. Depending on the diagnosis, treatment may consist of conservative care involving temporary immobilization, activity modification, physical therapy, and eventual return to activity. In refractory cases, surgical capsular repair or labral or capsular treatment may be necessary. In the presence of severe dysplasia or with progression to arthritis, periacetabular osteotomy may be considered. Traumatic dislocations may also require concomitant fragment excision or fixation.

ANATOMY

Embryologic development is critical to the subsequent development of some forms of instability. Once fused, the acetabular surface is oriented approximately 45 degrees caudally and 15 to 20 degrees anteriorly. Significant alterations in acetabular version or inclination, as well as its orientation relative to the femoral head or neck, can affect the joint capsule and ligaments. The suction effect that relies on joint congruency for its function may also be compromised. The variability of this orientation may be a factor in the development of hip instability and needs to be considered in any treatment algorithm.

Although relying largely on its bony anatomy, hip stability is complemented by the acetabular labrum and capsuloligamentous complex. In the neutral anatomic position, the anterior part of the femoral head is not engaged in the acetabulum. The acetabular labrum compensates for this by covering this portion of the femoral head. The labrum is attached to the transverse acetabular ligament anteriorly and posteriorly at the base of the fovea and proceeds to run around the circumference of the acetabular rim.¹ The labrum deepens the “socket” and aids in maintaining the suction effect that provides additional hip stability. Absence of the labrum can lead to a loss of this suction effect, as well as increased cartilage surface consolidation as a result of the loss of hydration, thereby increasing contact pressures.³^–⁵ Proprioceptors and nociceptors have been identified within the labrum and may explain the decreased proprioception and increased pain in the athlete with a torn labrum.⁶ Much like the meniscus in the knee, the labrum is largely avascular, except for the most peripheral portion near the capsule, limiting its ability to heal.⁷

The labrum is not, however, a stand-alone structure. It functions in conjunction with the capsuloligamentous complex. The fibrous hip capsule and its ligaments are like a thick sleeve. Anteriorly, this complex primarily consists of the iliofemoral ligament (ligament of Bigelow), a 12- to 14-mm thick structure shaped like an inverted Y. It provides resistance to hip extension beyond neutral and resists external rotation. The pubofemoral ligament, which arises from the pubic portion of the acetabular rim and passes below the neck of the femur to blend with the most inferior fibers of the iliofemoral ligament, reinforces the inferior and anterior capsules, resisting extension and abduction. The ischiofemoral ligament reinforces the posterior surface of the capsule and has a spiraling pattern. Finally, the zona orbicularis is a deep layer of fibers within the capsule that forms a circular pattern around the femoral neck, constricting the capsule and helping maintain the femoral head within the acetabulum.¹

The position of maximum hip joint stability is in full extension because it is in this position that the twisted orientation of the capsular ligaments causes a screw-home effect.¹ However, the articular surfaces of the hip joint are not in optimal contact in this position (the close-packed position). Optimal contact occurs in the loose packed position of flexion and lateral rotation as the ligaments uncoil. The greatest risk of traumatic dislocation, then, is when the joint is between the close-packed and maximally congruent position (flexed and adducted position). The ligamentum teres and psoas tendon are two extra-articular structures about the hip that deserve additional discussion. The ligamentum has no real stabilizing effect on the joint, whereas the psoas protects the anterior intermediate capsule, which is devoid of ligamentous protection.

CLINICAL EVALUATION

History

Making the diagnosis of hip instability can be a diagnostic dilemma. Hip instability can manifest as overtly as frank traumatic dislocation or can be as obscure as occult groin pain or clicking. Hip pain, clicking, or “giving way” in the young adult patient may arise from any number of anatomic structures. The picture can be further complicated by referred pain from the lumbosacral region as well as the genitourinary tract and abdominal wall.⁸ Age also plays a significant role in determining a differential diagnosis for hip pain.⁹ In children, hip dislocation, bony avulsions, apophyseal injuries, fractures, slipped capital femoral epiphysis (SCFE), Legg-Perthes disease, developmental dysplasia of the hip (DDH), and toxic and septic arthritis are all potential causes.⁹

The history should include a qualitative assessment of the main complaint to determine whether it is primarily pain, clicking, catching, or instability. A golfer may describe weakness in the involved leg while swinging for power. Pain may also occur after long periods of sitting, when getting out of a car, or rising from a chair. Timing of the onset of the complaint is also essential. Precipitating factors, as well as potential referred or systemic causes, must be assessed.

Physical Examination

Antalgic gait patterns in which there is shortening of the stance phase and step length on the affected side can result from instability. A Trendelenburg gait may indicate an attempt to bring the center of gravity over the affected side to decrease the moment arm across that hip joint.¹⁰ The patient with atraumatic instability may be able to demonstrate subluxation or dislocation of the involved hip, although this is rare.

Traumatic hip instability can manifest with pain on prone extension–external rotation of the involved hip. A positive axial distraction test can be confirmed with a positive vacuum sign on dynamic fluoroscopy (Fig. 7-1).¹ Anterior apprehension may also be elicited with the patient in the lateral decubitus position while suspending the affected leg in slight abduction (Fig. 7-2). The presence of a positive examination indicates capsular laxity in traumatic and atraumatic instability.

FIGURE 7-1 Suction seal effect of the joint. This is anintraoperative image of 16-year-old patient with repetitive use instability caused by high-level gymnastics participation. Minor axial traction (15 lb) causes significant distraction and subluxation of the joint.

FIGURE 7-2 Apprehension position. The patient is placed in the lateral decubitus position and the affected extremity is supported by the examiner. The examiner uses the other arm to push the hip in an anterior direction as pressure is applied over the posterior aspect of the greater trochanter. In symptomatic patients, a sensation of subluxation can sometimes be elicited, whereas in others, there is a reproduction of their pain.

In some patients, and with proper relaxation, a sense of the end range of capsular tightness and the end point of the ligamentum teres can be obtained by the supine external rotation test, in which the patient is placed supine and the affected leg is suspended in 30 degrees of flexion by the examiner. With gentle external rotation, while the patient is relaxed, the end point of external rotation can be assessed (Fig. 7-3). Also, a comparison can be made with the contralateral (and presumably normal) extremity. If there is a significant increase in external rotation as compared with the normal extremity, laxity of the Y ligament can be inferred. Also, if a large anterior labral tear exists, audible snapping and reproduction of pain can be elicited.

FIGURE 7-3 Supine external rotation. The patient is in the supine position while the examiner rests the affected extremity in both arms. Gentle maximal external rotation is performed on the leg while the patient attempts to relax. The total external range of motion should be assessed as compared to the contralateral extremity. In addition, a sense of the end point is also obtained.

Range of motion of the hip joint is also important to document. Supine external rotation should be measured in the normal and affected extremities. Also, rotation of the flexed hip varies with version of the acetabulum. In excessive anteversion, an excess of internal rotation is noted.

IMAGING

Imaging should always begin with plain radiographs. The standard views are a standing anteroposterior (AP) pelvic view, as well as AP and lateral views of the affected hip. Apart from being able to detect the common radiographic features of trauma, plain radiographs can also help detect femoroacetabular impingement.

Several radiographic indices have been described to differentiate normal from abnormal osseous anatomy based on the AP pelvic radiograph. The Tonnis angle is used to assess lateral subluxation of the femoral head and subsequent increased forces across the weight-bearing acetabulum (Fig. 7-4).¹¹ A measurement of less than 10 degrees is considered normal.

FIGURE 7-4 AP radiograph showing the technique of measuring the Tonnis angle (normal, <10 degrees). In this case, the red line (line 1) connecting the two ischial tuberosities is the reference line on which all other lines are based. The yellow line (line 2) is a line drawn parallel to line 1 through the center of the femoral head. The angle formed between line 2 and a third line connecting two points demarcating the sourcil or weight-bearing surface of the acetabulum is the Tonnis angle.

(Adapted from Delaney S, Dussault RG, Kaplan PA, et al. Radiographic measurements of dysplastic adult hips. Skeletal Radiol. 1997;26:75-81.)

The center edge angle of Wiberg assesses acetabular inclination (Fig. 7-5). This angle should measure at least 20 to 25 degrees to be considered normal.¹²^,¹³ One can estimate acetabular version using the AP pelvis by looking for a crossover sign (Fig. 7-6). The two lines involved estimate the posterior and anterior rims of the acetabulum. The posterior rim is traced from the ischial tuberosity superolaterally to the roof of the acetabulum. The anterior rim is traced from the teardrop in a superior and lateral direction along the rim to the roof. If these lines cross, it is estimated that the acetabulum is retroverted; if not, it is assumed that the acetabular version is within the normal 10- to 15-degree anterior version.¹⁴^,¹⁵

FIGURE 7-5 AP radiograph showing the measurement technique for the center edge angle of Wiberg. Line 2 is made through the center of the femoral heads. Line 3 is a line directly perpendicular to line 2, and the angle between this line and line 4 (a line from the center of the femoral head to the lateral edge of the acetabulum). This angle should be greater than 25 degrees, with 20 to 25 degrees being considered borderline.

(Adapted from Delaney S, Dussault RG, Kaplan PA, et al. Radiographic measurements of dysplastic adult hips. Skeletal Radiol. 1997;26:75-81.)

FIGURE 7-6 AP radiograph demonstrating the crossover sign indicating acetabular retroversion. Note that the red line (representing the anterior wall of the acetabulum) crosses the yellow line (representing the posterior wall of the acetabulum). Also of note is the visualization of the ischial tuberosity (blue line), which is normally superimposed by the acetabulum, but easily visible in the retroverted acetabulum.

When evaluating a patient with potential residual dysplasia, the faux profile view is often used to evaluate anterior and lateral coverage of the femoral head by the acetabulum. Although plain radiographs are sufficient for diagnosis in a number of cases, there are pathologic entities that require further investigation. Imaging of bony lesions about the hip is best accomplished using computed tomography (CT) because it provides the greatest spatial resolution of bony structures. Cases of questionable hip dysplasia should use CT in preoperative planning. The use of intra-articular contrast in CT arthrography can increase the contrast between cartilage and labral tissue.⁸

Magnetic resonance imaging (MRI) has become the most reliable means of diagnosing unresolved hip pathology in addition to direct visualization and is often useful in cases of instability. MRI has been shown to demonstrate inflammatory arthropathies and joint effusions effectively, but has been less accurate in assessing articular cartilage lesions.⁸^,¹⁶^,¹⁷ Contrast MRI studies in patients with a torn labrum or torn iliofemoral ligament can result in a larger volume of intra-articular contrast, and thus indirectly confirm the diagnosis of instability (Fig. 7-7).¹

FIGURE 7-7 MRI scan (T2-weighted coronal image) of a patient with hip instability secondary to excessive capsular volume. Also note the large labral tear that is evident in this image.

TREATMENT CONSIDERATIONS

Atraumatic Instability

As is the case in the shoulder, in which numerous types of instability have been described, the separation between traumatic and atraumatic instability in the hip is often difficult. For the purpose of this chapter, only those instability syndromes that are the direct result of a distinct traumatic event that caused a discrete subluxation or frank dislocation will be considered as traumatic instability. All other congenital dysplasias and connective tissue disorders, as well as repetitive use injuries and idiopathic syndromes, will be considered as atraumatic.

Congenital connective tissue disorders can predispose a patient to atraumatic hip instability. There have been very few reports in the literature of habitual hip dislocation that have not been accompanied by Ehlers-Danlos syndrome, arthrochalasis multiplex congenital, Marfan’s syndrome, Down syndrome, or congenital or acquired hip dysplasia.¹ As opposed to frank episodes of subluxation or dislocation that may be seen in atraumatic shoulder instability, idiopathic hip instability often presents with a more subtle pattern. In a review of five cases, a syndrome of idiopathic hip instability was described, in which all patients presented with a long history of snapping in the groin, gait disturbances, and pain in the provocative position of hip flexion, adduction, and internal rotation.¹⁸ Symptoms were alleviated by extension abduction and external rotation (maneuvers analogous to the Barlow and Ortolani signs), thus suggesting a posterior instability. When awake patients had their affected hip subjected to gentle manual traction, 4 to 10 mm of inferior subluxation was seen. The force used to subluxate the hip in these cases was much less than the 400 N of axial force described as necessary to create a radiographic vacuum sign of subluxation.¹⁹ All this evidence led the authors to postulate that subclinical hip dysplasia, combined with capsuloligamentous laxity, causes a break in the suction mechanism of the hip during gait, causing a popping sensation. Presuming that the instability was largely posteriorly directed and that preoperative arthrograms showed posterior capsular redundancy, one patient underwent open posterior capsular plication.

Atraumatic instability has also been attributed to a deficient labrum associated with redundant capsular or ligamentous tissue.¹ This deficient complex can create an abnormal load distribution caused by a transiently incongruent joint. The screw-home mechanism caused by the dynamic nature of the hip capsule and its associated ligaments may help explain why pelvic rotation and external rotation of the hip commonly elicit symptoms of instability. Professional and high-level athletes who participate in sports that require repeated hip rotation (e.g., football, golf, gymnastics) are susceptible to overuse injuries to the labrum and capsuloligamentous complex. Tears of the labrum or iliofemoral ligament can result in insufficiency and cause an increased tension on the joint capsule, which can be further exacerbated in patients with slight superior and lateral inclination of the acetabulum. In addition, cadaveric analysis of hip stability following capsular venting and a 15-mm labral tear has shown that positions of hip extension, when combined with abduction or external rotation, result in large strains in the anterior labrum.²⁰

Labral degeneration, combined with subtle rotational hip instability secondary to redundant capsular tissue in elite athletes, has been described. Ten patients were treated with arthroscopic labral débridement and thermal capsulorrhaphy. All patients had improvement in their Harris hip scores, with 83% having significant improvement in their symptoms at 12- to 24-month follow-up.¹ In contrast, Santori and Villar have reported only 67.5% success in 58 cases at a mean 3.5-year follow-up with labral débridement without capsular treatment.²¹ Alternatively, plication can also be performed by passing nonabsorbable, braided suture through the capsule, thus imbricating the capsular tissue (Fig. 7-8).⁷

FIGURE 7-8 Capsular redundancy of the right hip in a 16-year-old gymnast with no major macrotraumatic event. A, Arthroscopic view of right hip viewed from the anterolateral portal while in the peripheral compartment. The perilabral sulcus (arrow) is seen to be large. The labrum is relatively normal. B, View following capsulorrhaphy using suture anchors. Note the obliteration of the perilabral sulcus, with the suture in place immediately proximal to the acetabular rim.

Although subtle hip dysplasia combined with capsular laxity and labral pathology can lead to symptomatic hip instability amenable to arthroscopic treatment, care must be taken to recognize more significant dysplasias. Overtly dysplastic hips typically share common abnormalities that occur to a greater or lesser extent, depending on the severity.²² The true acetabulum is usually shallow, lateralized, anteverted, and deficient anteriorly and superiorly. There may also be underdevelopment of the entire pelvis. On the femoral side, the femoral head is usually small and the neck is usually excessively anteverted and short, with an increased neck-shaft angle. The greater trochanter may be displaced posteriorly and the femoral canal may be narrow.²³^,²⁴ The presence of significant hip dysplasia in the adult can be ascertained using primarily plain radiography.

A patient who presents with radiographic evidence of dysplasia but little or no symptomatology should be treated nonsurgically with strengthening and proprioceptive training of the hip and trunk musculature.²³ Nonsteroidal anti-inflammatory drugs (NSAIDs) can be used and combined with cessation of high-impact activities. The patient should be educated about the potential natural history of increasing instability and the potential development of degenerative arthritis.

Surgical intervention should be reserved for those patients who fail conservative management and have persistent symptoms. Arthroscopic treatment in the patient with significant dysplasia is not indicated. In addition, significant labral hypertrophy occurs in these patients. The role of this excess labral tissue has not been completely elucidated, but it may be significant in its effect on joint stability. Aggressive resection of this tissue can accelerate degenerative changes and possibly lead to premature degeneration. Pelvic and femoral osteotomies, arthrodesis, resection arthroplasty, and replacement arthroplasties have all been described as potential treatment options.²³ Osteotomies that may be expected to slow the progression of degenerative changes by distributing weight-bearing forces across the hip joint better have been described. These procedures may also provide better preservation of bone stock for potential subsequent arthroplasty (Fig. 7-9).

FIGURE 7-9 Periacetabular osteotomy. A, 19-year-old woman with history of hip pain and increasing disability. B, Postoperative radiograph following periacetabular osteotomy

Traumatic Instability

The most common mechanism for hip dislocation is a dashboard motor vehicle injury with a posteriorly directed force against a flexed knee and hip. During athletic activities, dislocations may occur via a forward fall onto a flexed knee with the hip flexed or a blow from behind while down on all four limbs (Fig. 7-10).²⁵^,²⁶ Sports such as American football, skiing, jogging, gymnastics, basketball, biking, and soccer have all had reports of traumatic dislocations (Fig. 7-11).²⁷^–²⁹ Excessive capsular laxity has been associated with these types of dislocations.³⁰^,³¹ Irrespective of the degree of initial trauma, if normal capsular healing fails to occur, persistent laxity may remain and predispose the patient to instability (Fig. 7-12). Two cases of posterior dislocation following minor trauma while playing soccer have been reported, probably secondary to large posterior capsular redundancy.³² Similarly, recurrent anterior dislocations have occurred as a result of excessive anterior capsular redundancy.³³ These patients have been treated nonoperatively with brief immobilization, physical therapy, and activity modification. Open capsular shift or repair has been particularly successful in preventing further dislocation.³⁴ Arthroscopic treatment of this type of capsular laxity using thermal capsulorrhaphy or capsular plication combined with labral débridement has shown promising early results while potentially avoiding the open surgical complications of heterotopic ossification and osteonecrosis of the femoral head.¹

FIGURE 7-10 Tear of the ligamentum teres following right hip subluxation. A, T2-weighted coronal image. The tear is seen at the inferior margin of the acetabulum (arrow). B, Arthroscopic view of ligamentum tear (arrow points to avulsed end). The view is from the anterolateral portal.

FIGURE 7-11 Labral tear following dislocation of the right hip in a 19-year-old college basketball player (viewed from the anterolateral portal). A, Note the significant synovial reaction (arrow) around the labral tearing. B, Focal femoral head defect (arrow) in the same patient.

FIGURE 7-12 MRI scan following right hip dislocation with no bony involvement. A, Torn posterior capsule; T1-weighted coronal image through the posterior aspect of the joint. The tear is seen longitudinally at the margin of the posterior labrum (arrow). To the right of the arrow is the posterior acetabular wall. B, T1-weighted axial image depicting a posterior capsulolabral avulsion (arrow).

Hip arthroscopy has been shown to be an important part of the armamentarium in the effort to at least delay the onset of post-traumatic degenerative joint disease (DJD) following traumatic dislocation.³⁵^,³⁶ Residual intra-articular bony or osteochondral fragments may be responsible for the development of DJD in complex dislocations. The incidence of osteoarthritis secondary to traumatic hip dislocation has been reported between 24% to 57%, depending on the severity of the trauma.³⁷ Simple dislocations (without radiographic evidence of fracture) have been shown to have the lowest incidence. However, the incidence of post-traumatic DJD in these injuries is still 24%.³⁸

Nonconcentric reduction after a traumatic dislocation is considered an absolute indication for operative intervention. The presence of loose bodies (LBs), however, has been considered a relative indication, particularly if the reduction is concentric and the LBs are located below the fovea.³⁵ An in vivo rabbit model has shown that free cartilaginous loose particles inside the joint increase chondrolytic enzyme activity and induce secondary arthrosis.³⁹ Because 24% of simple dislocations have been shown to develop subsequent DJD, the literature would support that LBs should be addressed prophylactically, and arthroscopy is an excellent vehicle for accomplishing this (Fig. 7-13).³⁸

FIGURE 7-13 Loose cartilaginous bodies in a left hip following dislocation in a collegiate basketball player. A, MRI scan (coronal T1-weighted image) reveals a cartilaginous loose body (arrow) not evident on plain films. B, View from anterior portal. A loose body is silhouetted by synovial tissue.

Mullis and Dahners ³⁶ have reported on a series of 36 patients treated with arthroscopy following dislocation. Excluding procedures in which a repeat arthroscopy was performed for retained LBs, the average time to surgery was 15 days. Of 36 patients, 25 (69%) had radiographic evidence of LBs (nonconcentric reduction and/or radiographically visible LBs). In 9 patients, there was a concentric reduction without radiographic LBs. Intraoperatively, 33 of 36 patients(92%) were found to have LBs. Of the 9 patients with no preoperative radiographic evidence of LBs, 7 (78%) had some found at arthroscopy (Fig. 7-14).

FIGURE 7-14 Loose bodies in the hip with nonconcentric reduction. A, CT scan through the center of the femoral head depicting multiple loose bodies within the joint. B, Intraoperative image of loose osteocartilaginous fragment that was removed.

In a 15-year experience with hip arthroscopy after traumatic dislocation, 10 joints in nine patients were treated 1 to 7 days postdislocation.³⁵ Seven hips were classified as Thompson-Epstein (TE) I injuries, two type II, one type IV, and one central fracture dislocation. All dislocations had arthroscopic lavage and débridement and 7 of 10 joints revealed previously unrecognized loose osteochondral fragments. At a minimum of 5 years follow-up, 8 of 10 joints were asymptomatic. One joint (Pipken type 3 femoral head fracture) went on to develop femoral head AVN that was not symptomatic. The one TE IV injury developed hip joint DJD at 1 year. These results prompted the authors to recommend arthroscopic débridement for all TE types I and II dislocations, but not types III and IV.

Philippon and colleagues ²⁶ have recently documented acute dislocations in 14 professional athletes. The findings of importance in their study were a significant association between dislocations and additional findings, including significant labral tears (100%), as well as multiple LBs and osteochondral injuries on the acetabular and femoral surfaces in 73% of cases. In addition, 73% had tears of the ligamentum teres. Finally, there were 9 patients (60%) who had evidence of femoroacetabular impingement by radiographic and arthroscopic evaluation.

There has been some concern regarding the timing of arthroscopy after traumatic dislocation in terms of the risk of avascular necrosis (AVN), prompting those concerned to recommend a 6-week waiting period postdislocation before performing arthroscopy. In two of the previously discussed series, however, arthroscopic surgery was performed in the first 2 weeks.³⁵^,³⁶ The only complications observed in the Mullis and Dahners study were three repeat procedures for retained LBs and some fluid extravasation into the gluteal compartment that resolved without incident. Although the possibility of extravasation and subsequent significant complication exists, it can be mitigated by keeping the pressure on the arthroscopic pump low (if one is used). Also, expeditious management of the pathology with limited exposure to inflow of fluid will avoid this issue. In cases in which extended surgical procedures are undertaken, it is important to palpate the abdomen and maintain a watchful eye on the patient’s vital signs to note any ongoing extravasation, particularly into the abdominal cavity.³⁶ Yamamoto and associates³⁵ had one case of AVN that developed in a patient with a Pipken type 3 injury.

SURGICAL TECHNIQUE

The standard hip arthroscopy techniques described in other chapters of this text will suffice with respect to positioning. Either the lateral or supine position is effective for dealing with the sequelae of dislocations, such as labral tearing and LBs. One critical element in the procedure includes an examination under anesthesia of both the affected extremity and the presumably normal contralateral hip. The decisions that need to be made refer to laxity of the capsular tissues, and whether there is a radiographic vacuum sign in those with atraumatic instability. Also, the direction of instability and positions of stability need to be documented.

A complete diagnostic examination of the hip joint is also critical and includes the peripheral compartment. There are many cases in which the central compartment diagnostic evaluation reveals only minimal trauma and possibly some chondral abnormalities, without any evident LBs. On entering the peripheral compartment, however, a loose body can be found and may be responsible for some of the mechanical symptoms that the patient is experiencing.

The first technique to discuss with regard to the challenges presented by dislocations is that of labral repair. A variety of techniques are available for repair of labral detachment; these are similar to the experience in the shoulder. The specific challenges presented by the hip include the limited maneuverability within the joint and sometimes the degree of damage to the labrum, precluding a good repair. The specific techniques have been described in the chapter on labral injury (see Chapter 3).

The issue of capsular laxity is of particular interest, especially in patients with atraumatic instability. The amount of laxity that is normal is difficult to quantify and there are no scientific studies to date that offer objective criteria with respect to imbricating the capsule. It has been my experience that those patients who have a significant radiographic vacuum under anesthesia or frankly subluxate with an examination under anesthesia (EUA) are those who warrant a capsular repair.

Once all the labral pathology has been addressed, the amount of capsular redundancy is assessed. It is important to assess the laxity over the area that is presumed to be abnormal based on the EUA and the mechanism of injury, if one is known. Most commonly, the anterior capsule is involved in atraumatic patients. The assessment and treatment of this problem are undertaken from the peripheral compartment with traction removed and the leg in approximately 45 degrees of flexion. To imbricate the capsule, an accessory portal needs to be established, in addition to the standard anterior and anterolateral portals. The portal that is typically established is termed the midanterolateral (MAL) portal and is established midway between the anterior and anterolateral portals, creating an equilateral triangle between the three portals (Fig. 7-15). This portal is used for manipulation of the sutures between portals.

FIGURE 7-15 This midanterolateral (MAL) portal was established midway between the anterior (A) and anterolateral (AL) portals. An equilateral triangle is formed between the two standard portals and the MAL. AAL, accessory anterolateral; ASIS, anterior-superior iliac spine; PL, posterolateral.

In the typical case, the imbrication is undertaken in a medial to lateral direction. In patients in whom there is a very large perilabral sulcus, a proximal to distal imbrication is technically simpler easier to accomplish (see Fig. 7-8). When a medial to lateral imbrication is undertaken, the first step is to isolate the capsule on both the intra-articular and extra-articular spaces. The extra-articular preparation is undertaken by pulling the arthroscope out of the capsule (arthroscope in the anterolateral [AL] portal). Once the scope is out of the joint, the anterior portal is used to elevate the soft tissues away from the capsule to visualize the area where the imbrication will take place. Once an area of approximately 2 cm² is cleared, preparation is made for suture passing. The anterior portal serves as the portal for delivery of sutures from outside the joint and the MAL serves as the portal to grasp the sutures within the joint. Using a suture penetrator device, one suture is placed through the capsule and grasped from the AL portal. The other limb of the suture is now passed through the capsule, approximately 1 cm more lateral than the first limb. This limb is retrieved through the AL portal and shuttled outside the cannula. A second suture is now passed proximally or distally to the first, depending on the configuration of the first suture. Once the two sutures are passed, the arthroscope is placed outside the joint again and the sutures are tied (see Fig. 7-8). Confirmation of appropriate tightening of the joint can be obtained by visualization of the joint through the AL portal.

PEARLS& PITFALLS

• Thoughtful assessment of radiographs

The most important consideration in any patient with a presumed unstable hip is to determine the degree of bony abnormality. In cases of mild dysplasia, there is certainly a good potential outcome with a properly performed arthroscopic stabilization. In cases of more severe dysplasia, consideration should be given to more complex (and open) procedures, including periacetabular osteotomies.

• Examination under anesthesia

Examine each patient under anesthesia prior to any instrumentation. The flexion, presence of a flexion contracture, or internal and external rotation at 90 degrees of flexion should all be documented in the affected extremity and presumably normal contralateral hip. In addition, fluoroscopic assessment of hip translation with gentle axial traction should be documented. Subluxation with less than 15 to 20 pounds of force is indicative of incompetent soft tissues. This patient should be considered for surgical stabilization through a combination of labral repair and/or capsular imbrication.

• Radiographic documentation of anchor position

When performing hip labral repairs, the position of anchor placement is significantly different than in the shoulder, where most surgeons already have experience. The angle is more acute, and the soft tissues do not allow angulation of the insertion tools as easily as in the shoulder. In addition, the acetabular cavity is concave in shape, as opposed to the convexity of the shoulder. Thus, fluoroscopic confirmation of the angle of entry of the suture anchor should be obtained. Oblique images should be used in questionable cases. Any image that shows the anchor trajectory within the acetabular fossa is indicative of possible joint penetration and should prompt the surgeon to redirect it.

• Assessment of peripheral compartment

The peripheral compartment is part of the hip joint. The area includes approximately 25% of the articular cartilage of the femur that otherwise is not seen if this compartment is not entered. More importantly, there are often LBs and sometimes labral tears, which are only seen from this vantage point. Finally, surgeons performing hip arthroscopy should be familiar with the normal variants that are seen in this compartment. When something outside the norm presents itself, the surgeon will know that there is an issue that needs to be considered in the treatment algorithm for that patient.