Groin pain in athletes: a novel diagnostic approach

Groin pain in a performing athlete can be very challenging to diagnose and treat. The differential diagnosis includes intra-articular causes, extra-articular causes and non-musculoskeletal causes. A detailed clinical and radiological assessment of groin pain in this group is critical and can identify the underlying pathology. Diagnostic hip block is a valuable tool to differentiate intra-articular causes from extra-articular causes. Hip arthroscopy can help in identifying some of the elusive intra-articular conditions, which were once undiagnosed and therefore, left untreated, resulting in premature ending of competitive careers. This article attempts to explore current thinking on evaluation of groin pain, particularly in young individuals, and to establish a simple protocol for a clinical and diagnostic approach to this difficult problem.


Introduction
Groin injuries account for 2% to 5% of all sports-related injuries with a high recurrence rate between 15% and 31% [1]. Inadequate evaluation of these injuries can result in premature ending of competitive careers [2]. Therefore, proper evaluation and appropriate treatment of groin pain particularly in a competitive athlete are paramount and can be very challenging [3][4][5][6]. Groin pain may result from an acute injury or repetitive trauma. Acute groin pain is commonly seen in sports that involve a sudden change in direction while running. In chronic groin pain, the ongoing complaints may be present for months to years [7].
There are no universally agreed guidelines on the clinical and diagnostic approach to recalcitrant groin pain. This article attempts to explore current thinking on evaluation of groin pain, particularly in young individuals, and to establish a simple protocol for a clinical and diagnostic approach to this difficult problem.

Anatomy of groin pain
The groin consists of the area where the abdomen meets the legs and includes the structures of the perineum. The following structures comprise the groin: lower rectus abdominis musculature, inguinal region, symphysis pubis, upper portions of the adductor muscles of the thigh, the genitalia, as well as the scrotum in males.
From an anatomical point of view, various causes of groin pain can be considered under the headings of intra-articular and extra-articular causes [8,9]. The intra-articular group consists of lesions arising within the ball and socket of the hip joint, while the extra-articular group includes conditions arising from outside the ball and socket joint [10]. Experts estimate that 60% of intra-articular injuries are initially misdiagnosed as extra-articular [11]. There have been a number of publications highlighting the presence and importance of these intra-articular injuries [12][13][14]. It is important to note that many conditions of non-musculoskeletal origin may have referred pain in the groin. These include gynaecological, urological, malignancies, sexually transmitted diseases and rheumatological conditions [15].

Approach to groin pain in athletes
The approach to athlete with groin pain can challenge the clinician for a variety of reasons as the cause of pain can be intra-articular, extra-articular or radiation from elsewhere [16]. The first step in evaluating the groin pain in young athletes is to obtain a thorough history followed by a detailed physical examination to avoid missing the diagnosis. The key to history taking and the physical examination is to narrow down the differential diagnosis to either intra-articular pain or extra-articular pain.
A history of clicking on movement of the hip may indicate intra-articular pathology like labral tear, loose body or snapping hip. Byrd described the ''C sign'' in which a patient cups his or her hand above the greater trochanter in order to describe deep interior hip pain [8,17]. Altered sensation or weakness together with a burning-type pain may indicate nerve entrapment. For example, obturator nerve entrapment is an uncommon condition, which causes pain in the region of the adductor muscles.
The physical assessment requires the exposure of as much of the groin and hip as permitted, in standing, supine and lateral position. A detailed examination of hip includes the following: inspection for anatomic irregularity; palpation of specific regions to localise tenderness [18]; assessment of the range of motion of the hip [19]; observation of the patient's gait; and evaluation of performance activities like sprints and jumps which exacerbate the athlete's pain.
Intra-articular pathology usually presents with painful restriction of movements of the hip. It is estimated that     27-90% of patients with groin pain have more than one coexisting injury [13]. Therefore it is possible for clinicians to diagnose and manage one injury, while a second injury may go unrecognised [20,21]. Extra-articular causes such as osteitis pubis, muscle strain, avulsion injuries, stress fractures and nerve entrapment may be excluded by the type of onset pain and localising the site of tenderness. Acute and chronic causes of groin pain must also be differentiated. Acute injuries are relatively easy to diagnose based on history and physical findings, whereas chronic pain may be due to more than one cause and Table 1. Differential diagnosis for intra-articular causes of groin pain in athletes.
Common intra-articular pathologies causing groin pain

Conditions
Findings Related references 1. Femoroacetabular impingement (FAI) • Sharp anterior hip pain with deep flexion, internal rotation or abduction.
• Limited internal rotation and adduction in flexion.
• Restricted terminal hip range of movements.
• Reduced range of motion.
• Limited range of movements.

Imaging studies
Plain radiograph of the hip remains the mainstay examination for most of the groin injuries ( Figure 1). It remains as a baseline investigation, providing bony definition and alignment ( Figure 2). Standardised radiographs are mandatory and should include the use of the correct film-focus distance and proper centring of the X-ray beam to prevent a false impression of altered joint morphology [23].
Ultrasound is a cheap, safe, quick and efficient tool providing exquisite soft tissue detail with the added advantage of providing a dynamic assessment. Dynamic ultrasonography seems to be a promising modality to exclude subtle hernias not detected by physical examination. Ultrasound has been reported to be also useful in diagnosing internal snapping hip syndrome (ISHS) caused by the iliopsoas tendon [16,24,25].
Magnetic resonance imaging (MRI) is a powerful tool, providing excellent spatial resolution, and delineation of soft tissue structures including muscles, tendons and cartilage. It is a very sensitive and specific imaging modality for diagnosing osteochondral injuries, soft tissue injuries and inflammation.

Nerve conduction studies
Nerve conduction studies and electromyography (EMG) are very useful diagnostic tools for potential nerve entrapment syndromes, causing groin pain [30, 31].

Diagnostic hip block
Fluoroscopic guided injections have proven to be an extremely valuable diagnostic and therapeutic test to localise groin pain of intra-articular origin [32,33]. This may be done under general anaesthesia to ensure accurate intra-articular placement of the needle and should be followed by a carefully structured physiotherapy assessment in order to establish the intra-articular source of pain. Although the duration and extent of relief are variable, fluoroscopically guided, intra-articular injections of corticosteroid and local anaesthetic should typically alleviate symptoms attributable to labral tears, synovitis, mechanical impingement and osteoarthritic changes. A failed response to a well-placed injection should prompt evaluation for occult, extra-articular sources of symptoms [34]. A positive response to an intra-articular injection has been shown to be a 90% reliable indicator of an intra-articular abnormality [35]. However, a negative response from an intra-articular hip injection may predict a higher likelihood of having a negative result from surgery [36,37]. The possibility of communication between the hip joint and iliopsoas bursa may exist and this needs to be assessed with MRI prior to the block [38].

Hip arthroscopy
Recent years have seen increasing number of hip arthroscopies being performed worldwide. Hip arthroscopy is now a very well-established procedure [39][40][41][42]. This endoscopic procedure not only helps to diagnose some of these elusive intraarticular causes of groin pain (Figures 4 and 5) but also helps to treat specific lesions within the joint. Table 1 shows the common intra-articular causes for groin pain in athletes with their clinical findings and related references. The common extra-articular causes for groin pain in athletes with their clinical findings and related references are outlined in Table 2. We follow a simple algorithm to approach recalcitrant groin pain in athletes as shown in Figure 6.

Summary
Groin pain in a performing athlete can be very challenging to diagnose and treat. The differential diagnosis includes intraarticular causes, extra-articular causes and non-musculoskeletal causes. A detailed clinical and radiological assessment of groin pain in this group is critical and can identify the underlying pathology. Diagnostic hip block is a valuable tool to differentiate intra-articular causes from extra-articular causes. Hip arthroscopy can help in identifying some of the elusive intra-articular conditions, which were once undiagnosed and therefore, left untreated, resulting in premature ending of competitive careers.