Traumatic Hip Instability

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The diagnosis of a traumatic hip injury is obvious in severe cases of dislocation. However, more subtle traumatic subluxation of the hip can occur with seemingly minimal trauma. The clinician should have a high index of suspicion for intraarticular injury even after minor trauma. A careful physical examination should be performed to differentiate intraarticular versus extraarticular pathology. Patients may also have concommitent soft tissue injuries such as chondral injuries, labral tears, and capsular injuries. Injury patterns depend upon the age of the patient and the competancy of the surrounding soft tissue. The most common mechanism for hip dislocations is a dashboard motor vehicle injury (high energy). However, in athletic competition, a forward fall on the knee with a flexed hip or a blow from behind while down on all four limbs can also produce these patterns (more low energy) [15].

Patients with traumatic hip instability caused by hip dislocations or fracture dislocations present in severe discomfort and are unable to move their lower extremity. Hip dislocations have been reported in American football, skiing, rugby, gymnastics, jogging, basketball, biking, and soccer [16-19]. On physical examination, patients will classically present with the hip fixed in a position of flexion, internal rotation, and adduction. A complete neurovascular examination should be performed, and care must be taken to check for the presence of a partial or complete sciatic nerve palsy before any closed or open manipulation of the hip. Although rare, team physicians need to be aware of this injury due to the potentially serious long-term sequelae and associated loss of playing time.

The radiologic workup after a presumed traumatic hip injury begins with plain radiographs including an AP view of the pelvis and AP and frog-lateral views of the affected hip. In many cases, this will provide a relatively definitive diagnosis such as an acute traumatic fracture, avulsion fractures, dislocation, subluxation, osteitis pubis, or degenerative joint disease. Additional views that are typically required include a crosstable lateral radiograph and Judet oblique films to further assess acetabular fractures that are noted on the AP pelvis. Once the diagnosis of a hip dislocation is made, a careful evaluation of the femoral neck must be performed to rule out the presence of a femoral neck fracture before any manipulative procedures are performed.

Management of a hip dislocation is divided into an initial phase of achieving a rapid reduction of the dislocation followed by a secondary phase, which focuses on performing definitive care [20]. The initial urgency of reducing a dislocated hip is to minimize long-term complications such as avascular necrosis (AVN). Closed reduction performed under 6 hours has been shown to reduce AVN rate [21]. Estimates of AVN following hip dislocation varies in the literature from 1% to 17% [21-23]. At times, to achieve a safe reduction, the resources of the operating room may be necessary such as adequate anesthesia and fluoroscopy. After closed reduction is performed, additional films usually include an AP view of the hip and a CT scan with fine (3 mm) cuts through the hips. The value of CT scanning is its ability to assess the femoral head and to demonstrate the presence of small intraarticular fragments. In addition, CT can better visualize the size, location, and displacement of any associated ace-tabular wall fractures. In the acute setting of traumatic hip dislocations, numerous studies have demonstrated that MRI may aid in the diagnosis of labral disruptions, femoral head contusions and microfractures, sciatic nerve injury, and intraarticular fragments [24,25].

Most hip dislocations sustained during athletic activities are pure dislocations with either no associated fractures or small acetabular rim fractures due to the relative low-energy mechanism. Thus, surgical stabilization is often not indicated. Active and passive range of motion (ROM) can begin as soon as comfort permits. Flexion greater than 90° and internal rotation greater than 10° is not permitted for 6 weeks [26].

Surgical management is warranted for most displaced acetabular fractures that involve the weight-bearing portion to allow early ambulation and to produce a stable and congruent joint and allow early motion/ambulation [27]. Giza et al [16] recently reported two hip fracture dislocations sustained during soccer that involved 20% to 40% of the weight-bearing portion of the posterior wall of the acetabulum that required open reduction and internal fixation. Examination under anesthesia with stress testing of the hip is warranted if there is any question regarding the size and significance of posterior wall injuries.

Recently, hip arthroscopy has become a new adjuvant to open surgery to address femoral head pathology, chondral injuries, loose bodies, and labral pathology. Its role is not well defined and the optimal timing of the procedure is debatable given the concern of placing a hip in traction too soon after a dislocation. We feel that hip arthroscopy should be delayed for at least 6 to 12 weeks so that a repeat MRI can be performed to rule out the presence of early AVN before placing the patient into traction.

Traumatic posterior hip subluxation has recently received increased attention because it is a potentially devastating injury that may be misdiagnosed as a simple hip sprain or strain. Similar to hip dislocations, the mechanism is most often a fall on a flexed hip and knee with a posteriorly directed force being transmitted through the hip joint [28]. Due to less energy, the hip subluxates rather than dislocates. Physical examination usually reveals painful limitation of hip motion [28]. Unlike dislocation, hip subluxation has a more subtle presentation, and a high index of suspicion is necessary to avoid missing the diagnosis.

Patients who have sustained a hip subluxation often have normal radiographs or they demonstrate nonspecific changes. Moorman et al [28] performed Judet radiographs, which demonstrated posterior acetabular lip fractures in seven patients who sustained a posterior hip subluxation during American football. They have recommended that the radiographic workup of a patient who has a suspected hip subluxation should include radiographs of the hip, including oblique radiographs to evaluate for a "posterior lip fracture." The role of MRI is growing increasingly more important in the evaluation of traumatic instability. Moorman et al [28] performed MRIs on seven American football players suspected of having traumatic posterior hip subluxation, and defined a characteristic triad of findings including a posterior acetabular lip fracture, an iliofemoral ligament disruption, and a hemarthrosis. Patients typically will have an effusion in the hip joint as well as bone marrow edema in the region of the acetabular lip fracture. The presence of a significant hemarthrosis may push the treating physician toward fluoroscopic aspiration to decrease intra-capsular pressure (Fig. 6). Commonly, nondisplaced posterior wall injuries are present, analogous to a bony Bankart lesion in the shoulder. MRIs will typically demonstrate disruption of the iliofemoral ligament, confirming that the anterior structures are torn as they are placed on tension during the posterior subluxation episode. In our experience, the entire anterior capsulolabral complex may be injured involving both the iliofemoral ligament as well as the anterior labrum. Chondral shear injuries to the femoral head may also be seen, and an MRI can help to identify the presence of large cartilaginous loose bodies floating in the central and peripheral compartments, potentially pushing the treating physician toward arthroscopic removal (Fig. 7A-D).

Fig. 6. MRI of collegiate football player who sustained a posterior hip subluxation event resulting in significant hemarthrosis. This patient was taken for urgent aspiration under fluoro-scopic guidance.

MRI is also a useful tool to detect AVN. Although MRI is not an accurate predictor of AVN in the acute setting, a repeat scan usually should be performed at 6 weeks. If patients have no evidence of osetonecrosis at 6 to 12 weeks, they may return safely to sports activity. Those with evidence of osteonecrosis are at increased risk for subsequent collapse and joint degeneration, and the treating physician should caution the athlete about the risks associated with return to contact sports [28,29]. A general treatment algorithm for the management of athletic hip subluxation or dislocation is outlined in Fig. 8.

The last question that remains is what happens to athletes with untreated hip dislocations or subluxations? Athletes that sustain acute hip dislocations or

Unstable Chondral Lesion Mri
Fig. 7. MRI of a recent posterior subluxation event demonstrating posterior rim injury (A), anterior capsulolabral injury (B), chondral shear injury to the femoral head (C), and chondral loose bodies in the peripheral compartment (D).
Mri The Prostate

subluxations may develop chronic instability. Several papers have cited hip capsular laxity associated with previous hip dislocations [30-32]. Liebenberg [33] described two cases of recurrent posttraumatic hip dislocations that both had initial posterior dislocations sustained during football. The first patient had his first dislocation occur on the football field when he was 16 years old, which was followed by two subsequent hip dislocations with minor trauma. Arthro-graphy after the third dislocation revealed a posterior capsular lesion, and thus, the patient underwent surgery before the introduction of hip arthroscopy. During this open procedure, the labrum was identified and found to be retained at its attachment to the acetabular margin. However, there was attenuation of the capsular fibers, which allowed abnormal mobility of the labrum in a proximal to distal direction. Repair of the capsular defect was performed by excising the synovial pouch and by a "double-breast" repair of the lower part of the capsule over the upper with silk sutures. The second patient also sustained the first dislocation during football and then dislocated four subsequent times with minimal trauma. This patient also underwent open surgery and, again, the labrum was still attached firmly to the acetabular rim and the capsule was repaired with silk sutures. The authors concluded that a broad defect in the posterior capsule allowed the femoral head to dislocate and that obliteration of the pseudocavity by capsular repair appeared to be an adequate solution to the problem.

Other reports have also associated the presence of excessive hip capsular laxity and labral injury associated with previous hip dislocations or subluxation

Suspected Posterior Hip Subluxation/Dislocation

History and Physical Examination

Plain radiographs including Judet films / URGENT REDUCTION if dislocated

Posterior Rim Acetabular fracture

CT scan

Consider ORIF if > 30% of wt. bearing surface

Consider Stress Testing if < 30%

Normal

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