JF Baker, KJ Mulhall
Department of Orthopaedic Surgery, Mater Misericoriae University Hospital, Eccles St, Dublin 7
Abstract
There has in recent years been a fundamental change in the understanding of hip pain in the young adult and hip pain without plain radiographic findings of arthritis. Pain in these groups has long represented a diagnostic and therapeutic challenge. With new appreciation of hip biomechanics, pathological processes and the arrival of modern imaging modalities we now have a greater understanding of non-arthritic hip pathology. One of the commonest yet least well recognized ‘new’ diagnoses around the hip is femoro-acetabular impingement (FAI). FAI is a developmental condition of the hip joint that is associated with abnormal anatomical configuration and thus joint mechanics on either the femoral or acetabular sides or both. It is hypothesized to have a variety of precipitants and may ultimately lead to labral and chondral injury and what has previously been referred to as ‘primary’ or ‘idiopathic’ hip osteoarthritis1.
Introduction
Degenerative diseases affecting the hip typically present with groin pain, sometimes knee pain, accompanied by characteristic changes on plain x-ray. Less easy to diagnose and treat are patients presenting with ischial, trochanteric and groin pain, but with conventionally normal x-rays. These individuals are often given a musculoskeletal diagnosis that has been vague or inaccurate2.
Non-arthritic hip pathology
Pathological processes can result in damage to the articular surface or the acetabular labrum. Tears of the labrum (Figure 1), a structure that contributes to stability and force distribution within the hip, can be acute or chronic and like a torn meniscus in the knee can cause mechanical symptoms and pain3. The labrum blends with articular cartilage at what has been termed the ‘watershed area’4. At this point the articular cartilage can be sheared off subchondral bone and the labrum can be undermined. This can cause degeneration within the joint proceeding to osteoarthritis if unchecked5. Some have proposed that labral defects allow excess fluid into the hip articulation and are responsible for delamination of articular cartilage from subchondral bone6,7. A consistent finding in our practice and in published literature is the failure to detect early degeneration of the articular surfaces, not only on plain x-rays, but also routine magenetic resonance imaging (MRI).
Figure 1: labral tear at the ‘watershed’ region
Femoro-Acetabular impingement
Femoro-acetabular impingement (FAI) refers to a mechanical disorder resulting from anatomical abnormalities on either the femoral head and neck (Cam-type), acetabulum (pincer-type) or often, a combination. It is a potential precursor to osteoarthritis (OA) and many cases traditionally considered primary OA may well be secondary to FAI1. Cam-type impingement results may be a primary abnormality or a result of previous disease such as slipped upper femoral epiphysis (SUFE), Perthe’s disease, developmental dysplasia of the hip (DDH) or malunion of a femoral neck fracture. This lesion is more common in young athletic males and usually presents in a subacute fashion. Pincer impingement refers to over-coverage of the femoral head by the acetabulum. This may be due to coxa profunda or a retroverted acetabulum and is more common in older women. Both types of FAI leads to early abutment of the neck and acetabular edge, reduced free range of movement, abnormal intra-articular forces and shearing of articular cartilage. FAI lesions thus contribute to damage and ossification of the labrum, early degenerative change within the hip and ultimately an arthritic joint6.
Figure 2: A simplified schema of FAI: a normal configuration of the hip is shown (A). A Cam lesion (B) effectively increases the diameter of the femoral neck while a Pincer lesion (C) reduces the distance the femoral neck has to travel before full-range is complete.
Diagnosis
While classically hip pathology presents with groin pain, we understand now that early disease may present with buttock/ischial pain or pain over the greater trochanter. Patients may display the ‘C’-sign (Figure 3). Delayed diagnosis is a problem in our experience and others. In one series the delay to diagnosis was on average over 3 years with over 10% of patients having surgery at another site before FAI was diagnosed2. Specific tests for impingement include the FADIR (flexion, adduction and internal rotation) and occasionally FABER (flexion, abduction and external rotation). In the first, while the patient is supine, the hip is flexed to 90o and then adducted and internally rotated. Although these are always positive with clinically relevant impingement, they are not specific and can be positive in many intra-articular conditions. Clinician experience is helpful but further investigations are essential in definitive diagnosis.
Figure 3: Demonstration of the ‘C’-sign – the thumb and index finger are placed on the lateral thigh at the level of the greater trochanter in an attempt to locate the centre of the pain.
Plain x-rays may reveal a Cam lesion on the femoral neck (seen on special lateral views). ‘Pistol grip deformity’ is used to describe the abnormal appearance of a Cam lesion seen on the antero-posterior view of the hip, but it is typically not the lateral shoulder of the femoral head that causes most of the symptoms and signs8. Aside from basics, many parameters used to assess changes on x-ray are difficult to apply and reproduce9. Plain MRI alone can show labral tears or associated paralabral cysts, although it is poorly sensitive for tears and is not effective in detecting low grade or early damage to the articular surface. MR arthrography is much more sensitive for tears of the labrum and significantly more sensitive for articular or chondral surface changes although this latter defect remains difficult to demonstrate10. Our experience is consistent with these reports with many patients having significant chondral lesions and occasionally labral tears only diagnosed intra-operatively.
Treatment
Management of symptomatic FAI has been demonstrated to be beneficial in the short-term and future longitudinal studies will define the utility of this surgery in the possible prevention or deceleration of hip arthritis11. The only possible conservative option is major activity restriction which, in our experience, is difficult for young or athletic individuals to accept. Surgical treatments include open hip surgery, which is often suitable for the sequelae of paediatric conditions and more severe ‘primary’ deformities, or arthroscopic techniques. Hip arthroscopy is suitable for treatments such as resection of Cam lesions, removal of osteochondromas, labral repair or debridement and removal of loose bodies5,12. These procedures had previously warranted open arthrotomy, with or without hip dislocation, and a significantly longer rehabilitation period13. Excellent results have been reported in the literature with medium sized series of athletes undergoing arthroscopic management of labral pathology and FAI14,15. Although not suitable in all cases, hip arthroscopy has the benefits of short hospital stay (typically a day-case or overnight-stay procedure) and quicker rehabilitation. In cases with more marked deformity, such as sequalae of Perthes, growth disturbance and SUFE, we feel open surgery is indicated as it allows comprehensive access to the whole joint and thus more accurate and extensive anatomic and biomechanical reconstruction,
Our experience to date
We performed a review of 250 consecutive patients having hip surgery following initial presentation with symptoms and signs of impingement or hip pain with conventionally normal x-rays. 221 patients underwent hip arthroscopy for a variety of indications including isolated labral tears, osteochondral defects, removal of osteochondromatoses, a small number for diagnostic purposes and for resection of an impingement lesion with treatment of associated chondral and labral defects. 11 have undergone open resection of symptomatic impingement lesions while the remaining 18 have required a surgical dislocation of the hip for treatment of acetabular and femoral impingement lesions with associated chondral defects and labral repairs.
Although in our experience the results of open procedures overall have been good, they have potential for complications, with a non-union of an osteotomy and three screw removals in our series. This reflects the more extensive and aggressive nature of that surgery and we are increasingly reserving that approach for younger, more severely affected patients as described above. Complications from arthroscopic interventions are usually limited to temporary discomfort from traction devices and local paraesthesia with no neurovascular defect or infection to date. Over one-third of our cohort had grade III-IV chondral defects (the latter representing full thickness cartilage loss) at time of surgery that were not evident on pre-operative imaging16. Advanced lesions are more difficult to treat and predictably patients with these defects fared worse at follow-up than those with lesser defects17. Potential contributors to this high proportion of advanced lesions include patient reluctance to present to a physician or delays in referral (particularly when initial imaging demonstrates a ‘normal’ hip) while other diagnoses are pursued, indicating a need for a high degree of clinical suspicion.
We have found the predominant subpopulation presenting with FAI is the young, athletic male. Among these individuals GAA (football and hurling) is over-represented as a sporting code. One hypothesis is that this is due to repetitive torsional forces, and extremes of combined adduction and flexion, through the hip when kicking or performing twisting maneuvers in those with an underlying anatomic predisposition.
Interestingly, 6% of female patients had symptom onset during pregnancy – a previously unreported association without a definitive aetiology.
The future
Given our experiences to date, there is a need for increased awareness of FAI in young patients with significant hip pain2. This will allow prompt investigation and management with the possibility of both improving acute symptoms and also slowing or preventing further degeneration of the hip and, potentially at least, deferring the need for total hip arthroplasty. As techniques continually improve we can expect increasingly effective surgical and regenerative solutions for these patients. Such improvements can be expected to greatly improve patient outcomes and lessen the current increases being seen in arthritic hip conditions.
Correspondence: KJ Mulhall
Suite 4, Sports Surgery Clinic, Santry, Dublin 9
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