Hip Arthroscopy—Capsulorrhaphy for Laxity Syndromes

Amelia A. Sorensen

Matthew V. Smith

The hip joint is inherently stable because of the depth and conformity of the articulation between the femoral head and the acetabulum. The osseous anatomy, the ligamentous capsule, the ligamentum teres, the hip musculature, and the acetabular labrum provide additional stability to the joint (1,2,3). Historically, hip instability has been associated with traumatic causes like hip subluxation or dislocation. More recently, there has been greater awareness and appreciation for atraumatic causes of hip instability that result in refractory hip dysfunction (4). Atraumatic hip instability may result from redundancy or incompetence of the soft tissues around the hip caused by acetabular dysplasia, connective tissue disorders like Ehlers–Danlos syndrome, and microtrauma resulting from repetitive twisting activities.

Conservative treatment consisting of activity modification, oral anti-inflammatories, muscle strengthening, and injections remains the primary treatment for all causes of hip instability. Open capsular plication has been described for treatment of traumatic hip instability (5). With recent advancements in hip arthroscopy, hip capsular plication has become more common (1).

Anatomy

The osseous anatomy provides significant stability to the hip joint with the acetabulum covering between 77% and 79% of the total area of the femoral head (6). The average natural anteversion of the face of the acetabulum is 21 degrees and average natural abduction is 40 degrees (7). The shapes of the femoral head and acetabulum are more similar to conchoids than spheres with incongruity at the periphery (8). The shape and inclination of the acetabulum create more osseous coverage posteriorly. Conversely, anterior stability relies more on soft tissues, particularly the labrum and iliofemoral ligament (9,10).

The soft tissues surrounding the hip joint, such as the ligaments, labrum and muscles, act as important stabilizers of the hip. The ligamentous capsule surrounding the hip provides stability throughout the range of motion (ROM). External rotation is limited by the iliofemoral ligament (Y-ligament of Bigelow) (11). It originates near the base of the anterior-inferior iliac spine and then splits into two arms. The lateral arm inserts on the anterior greater trochanter with the medial arm inserting on the anterior femur at the level of the lesser trochanter (12). The iliofemoral ligament also acts as a significant restraint to anterior translation of the femur during extension (13). The ischiofemoral ligament originates on the ischial acetabular margin and inserts on the base of the greater trochanter. It is located in the posterior portion of the capsule. It resists internal rotation in flexion, extension, and adduction as well as posterior translation (11,14). The pubofemoral ligament, which originates on the superior pubic ramus and then joins the iliofemoral ligament, resists external rotation in extension (11). The deep arcuate ligament, which is also located in the posterior portion of the capsule, resists extremes of flexion and extension. Inferior distraction forces are resisted by the proximal and middle parts of the capsule, which includes the zona orbicularis (15). The ligamentum teres has been shown to be taut in external rotation, flexion and adduction, and lax in internal rotation (16). Increased adduction has been seen after sectioning of the ligamentum teres; however, the overall change was small (17). The ligamentum teres’ contribution to stability has not been confirmed.

The acetabular labrum is a fibrocartilaginous structure that outlines the acetabular rim, adding depth and increasing the area of femoral head coverage. Both the deepening of the acetabulum and increased overall volume of the acetabulum enhance joint stability (18). Stability is also enhanced by the presence of a fluid seal that generates a “suction effect” by obstructing the flow in and out of the joint, thus increasing the negative intra-articular pressure (19). In addition, the labrum potentially contributes to stability by acting as a direct mechanical block (9,13). Removal of 2 cm or more of the anterior labrum has been shown to decrease the stability of the hip (20). Last, muscle forces surrounding the
hip generate joint compression. With the hip in extension, the iliopsoas and rectus femoris muscles act as dynamic stabilizers (21).

Disorders Associated with Capsular Laxity

Capsular laxity in the hip can be a consequence of either traumatic or atraumatic causes. Traumatic dislocations usually are the result of a clearly defined episode with an acute onset of pain. In contrast, atraumatic dislocations present with an insidious onset of symptoms. In either case, the events surrounding the onset of symptoms can provide clues to the reason for the underlying sense of instability.

Traumatic Hip Instability

Mechanism of Injury

Traumatic hip instability typically results from a clearly defined episode of subluxation or dislocation. Posterior dislocations are the most common and are caused by a posteriorly directed force transmitted through a bent knee, often occurring in a motor vehicle accident or other high-energy trauma. Other traumatic causes include falling onto a knee while in a flexed position with the hip adducted, getting hit from behind when down on all four limbs resulting in an external rotation force, or running with a sudden change in direction resulting in traumatic hip subluxation and dislocation (22). Two percent to five percent of dislocations are estimated to occur during sports activities (23). Athletes who participate in football, rugby, bicycling, skiing, dancing, hockey, gymnastics, biking, and soccer have all been shown to be at increased risk for traumatic instability (24,25,26).

Anterior hip dislocation occurs with forced abduction, external rotation, and extension usually in association with high-energy injuries as in motorcycle accidents (27). There have also been reports of iatrogenic anterior hip dislocation after hip arthroscopy, which has led to the recommendation that the capsulotomy be as small as possible when performing arthroscopic procedures within the central compartment of the hip (3). Furthermore, in patients with ligamentous laxity or large capsular defects, capsular repair and/or plication should be considered to minimize the chance of recurrent dislocation (28).

Clinical Presentation

The inciting event and clinical presentation of a patient who has a traumatic dislocation is usually clear. Patients usually present with an acute onset of severe pain and difficulty moving the involved hip. The resting position of the affected leg can help identify the direction of the dislocation. In the event of a posterior dislocation, the hip is slightly flexed, adducted, internally rotated, and shortened. In comparison, when dislocated anteriorly, the hip is extended, abducted, externally rotated but may not be shortened (29).

In contrast, patients who have a traumatic subluxation event may have a brief episode of severe pain that improves once the hip spontaneously reduces. Often these patients will have increasing discomfort and stiffness in the hip shortly after the injury because of bleeding into the joint. Patients may hold their hip in mild flexion, abduction, and external rotation (FABER) to reduce pain because this position decreases capsular tension when there is bleeding into the joint. Patients will often have severe discomfort with motion despite a congruent reduction on radiographs. A careful assessment of the event that caused the injury and attention to the patient’s subjective complaints will confirm suspicion for traumatic subluxation.

Radiographic Evaluation

Standard radiographic assessment of the pelvis and the affected hip should include an AP pelvis and cross-table lateral views. Judet views can be obtained to evaluate the acetabulum for fracture. A computed tomography (CT) scan can be helpful in cases of traumatic hip dislocation with an associated acetabular fracture. A CT scan can also be helpful if there is concern for an incarcerated joint fragment after hip reduction. In addition, a high percentage (9/14) of athletes who experience a traumatic hip dislocation have been found to have femoral acetabular impingement on radiographs (26). Therefore, acetabular inclination and version should be assessed in all patients with a suspected traumatic subluxation. The McKibbin index is defined as the sum of the angles of femoral and acetabular anteversion. A total of more than 60 degrees of combined femoral and acetabular anteversion denotes severe instability, because of the resultant stress on the anterior capsulolabral structures (30). Surgery for these conditions must balance increasing joint stability and decreasing intra-articular impingement.

An MRI or MR arthrogram can be used to assess for chondral injuries, loose bodies, labral tears, ligament disruption, subtle changes in the capsulolabral structures, femoral head contusions, and other soft tissue injuries (31). MRI should be obtained at 6 weeks after the injury to evaluate for avascular necrosis (AVN) with possible repeat MRI at 4 to 6 months if the diagnosis of AVN is suspected (32). In addition, any patient with pain or mechanical symptoms should be evaluated with an MRI or MR arthrogram to assess for associated labral tear, cartilage injury, or loose bodies that may not have been evident on plain radiographs or CT scan.

Treatment

Traumatic dislocation should be urgently reduced to limit the risk of AVN and to decrease pain. There is an increased risk of AVN if a hip remains dislocated for more than 6 hours (33). After reduction, stability should be evaluated with passive ROM while the patient is sedated. If there is any concern for compromised stability, the hip can be further evaluated with stress radiographs. A postreduction AP of the pelvis should be obtained to evaluate for concentric reduction. A CT should be routinely ordered to evaluate fractures of the acetabulum, femoral head and neck fractures and to evaluate for any intra-articular loose bodies. Surgery is indicated with the presence of an acetabular rim
fracture (>25% to 30%), an incarcerated intra-articular fragment, or if a concentric reduction is not maintained after a closed reduction. Hip arthroscopy or open surgical dislocation is indicated if there is osteochondral injury to the femoral head or if symptomatic loose bodies are present in the joint (34).

If surgical intervention is not required, active and passive ROM exercises should be started immediately. Following posterior hip dislocations, the patient should not flex the hip beyond 90 degrees or internally rotate more than 10 degrees for 6 weeks. After anterior hip dislocation, the hip is protected from hyperextension and external rotation for 6 weeks. Bracing is typically not needed for either type of dislocation. In both cases, the patient is often limited to toe-touch weight bearing for 2 to 6 weeks. However, long-term studies have failed to demonstrate a decrease in osteonecrosis or outcomes with protected weight bearing (35). An MRI should be obtained at 6 weeks after the injury to evaluate for AVN and to assess for loose bodies not evident on radiographs or CT. Patients can safely return to all activities, including sports, if no signs of AVN are present at 6 weeks. If early signs of AVN are present, patients can be treated with an additional 6 weeks of protected weight bearing and counseled to end their participation in sports.

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