Nothing ruins good results as valid follow-up!

The lack of reliable, valid and responsive outcome measures for patients with hip and groin injuries has, in our opinion, been one of the main reasons why very few treatment advances have been made within this field.5–9 ,18 ,19 While some existing treatments (based on case series) may have promise, their success has mostly been evaluated by treatment providers (often the operating surgeon and main author), instead of being evaluated by the treatment receivers (the patients). This makes it very difficult to get a true impression of these procedures’ potential effect. It is possible that patients’ perceptions of the treatment success of these interventions are entirely different from those of the treatment providers.20

However, with the recent development of reliable, valid and responsive outcome scores, such as the Copenhagen Hip And Groin Outcome Score,19 ,21 it is now possible to objectively evaluate patient-reported hip and groin symptoms and function.19 Furthermore, the development of reliable clinical tests, including hip strength, squeeze tests22–26 and specific hip range of motion tests,22 ,27 makes it possible to measure  some of the clinical impairments frequently presenting in this patient group.22 ,27–30 Further research into specific strength testing positions and contraction modes is needed, but so far it looks as if both substantial isometric and eccentric strength deficits (15–30%) exist across different hip and groin conditions.28–30

Different terminology from continent to continent, and country to country

When studying the international sports medicine literature, and travelling in different countries and continents, we have met many different approaches and opinions regarding the diagnoses and terminology. However, even though very different diagnoses and terminologies are often used, they very often seem to be based on very similar clinical symptoms, findings and premises. A good example of this is the commonly used term ‘groin strain’, which is considered by some to be a specific acute muscle–tendinous injury in the adductors.31 ‘Groin strain’ has been defined as pain on palpation of the adductor tendons and/or the insertion on the pubic bone, and groin pain during adduction against resistance,31 the exact criteria used to define adductor-related groin pain.2 ,32 The diagnosis of osteitis pubis adds to the confusion. Osteitis pubis is also characterised by pain when palpating the pubic bone.33 ,34 Sometimes, it also includes pain on palpation of the adductors.34 These obvious similarities suggest that some of these different terms may actually represent similar clinical scenarios.2 ,32–34 Furthermore, terms such as sports hernia and athletic pubalgia are often used without referring to specific clinical findings or definitions, making it impossible to ‘recognise’ these patients clinically or reproduce the studies they have participated in.1–3 10–15 The clinical diagnosis of sports hernia has mainly been made on the basis of surgical findings during groin hernia repair.10–15 However, the relationship between the symptoms and clinical findings and pathologies found at surgery needs to be better established in the future.

Multiple and complex pathologies—are we up for the challenge?

The major challenge in hip and groin injury research is the many different pathological conditions that seem to exist in this region.1–3 For most long-standing groin and symphyseal pain (>6 weeks),7 specific pathological understanding of its nature and aetiology is not well established.35 Using diagnostic imaging, pathology has especially been suggested to originate from either the adductor muscle tendinous insertional complex,36–38 the underlying symphyseal bone33 and/or the symphysis joint.39 ,40 Age and activity have previously shown to be associated with degenerative findings in the pubic symphysis.41 ,42 However, since no matched controls are included in these studies, it is not possible to conclude whether these findings are pathological or merely age-related and/or activity-related changes. Other important anatomical structures such as the hip joint, the iliopsoas tendon and the pubic attachment of the abdominals (rectus tendon and/or conjoined tendon) are also thought to be involved in patients with long-standing hip and groin pain.1–3 ,43 ,44 Basic research of the underlying anatomy is of great importance, as the location of the injury may depend on precision and testing specificity when interpreting findings from clinical examination and diagnostic imaging in the groin region. There is a insertional proximity between the adductor longus tendon and the rectus abdominal aponeurosis with interdigiting fibres attaching to the same aponeurotic plate, possibly also including other adductor and abdominal muscles.43–46 Knowledge and understanding of anatomy and histology in this area are therefore essential for the diagnosis. In a study from 2008, using MRI and clinical examination, Zoga et al 47 found that around 60% had rectus abdominis insertional injury. This observation is, however, not in agreement with findings from our centre where only a small proportion of patients was identified as having abdominal-related groin pain, including pain on palpation and isometric contraction (1–2%).2 However, in the study by Zoga et al,47 criteria for determining when rectus abdominis insertional injury, or any of the other specific types of groin injury mentioned in the paper, exist on MRI or clinical examination were not defined or described.47 Unfortunately, this is very often the case in the athletic groin pain literature.48

So, are we talking about differential diagnoses? Or are we just naming the same pathological condition differently? More research on homogeneous and well-described patient groups linking standardised, well-defined and reproducible clinical criteria with precise diagnostic imaging methods, following standardised protocols, with good intraobserver and interobserver reliability, is certainly needed.

The Copenhagen approach—using clinical entities as a classification tool

Acknowledging the fact that the exact pathology is still not fully understood,35 we have proposed a clinical examination and a classification tool.2 ,32 This approach focuses on differentiating between clinical entities based upon knowledge concerning anatomy, biomechanics and physiology, where specific muscle–tendon–bone complexes are sought to be isolated and investigated by palpation, muscle contraction and/or stretching, in order to identify the possible anatomical structures involved in the patient's ‘known pain’. Furthermore, other specific tests exist where the hip is stressed in flexion and extension, including specific compressive and rotational components.49 ,50 However, the intertester reliability of these hip tests needs to be improved. As an example, κ values of only 0.40–0.60 have been reported for the flexion—adduction—internal rotation test and the flexion—abduction—external rotation (FABER) test.49 ,50 One of the other main problems in this area is that some tests, while named the same, are performed differently. For instance, the FABER test is sometimes evaluated as being positive when the patients report that the procedure elicits the ‘known pain’ from the hip,50 ,51 whereas others describe a decreased range of motion (compared to the unaffected side) as a positive FABER test.50 ,52

Diagnostic imaging (x-ray, ultrasound and MRI) at our centre is only used for differential diagnosis, as the exact pathology is not known at present.35 These modalities are mainly used to avoid missing acute, specific and severe pathology. Furthermore, diagnostic imaging is of particular relevance when specific intra-articular hip joint pathology is suspected.35 When specific pathology is not identified, we use the clinical entities as our main clinical classification tool and communication form.2 ,32 The clinical entities approach that we use has been shown to be intratester and intertester reliable, and therefore provide the base upon which we classify our patients, and what specific anatomical structures we target as part of our treatment.2 ,32 Adductor-related groin pain seems to be the most frequent clinical entity we encounter,2 and this term now also seems to have been endorsed by others.36–38 ,53 Further research should focus on the underlying pathology behind this clinical entity approach to gain specific insight into the pathophysiological processes that future interventions should address. While an understanding of the pathological process is important in order to specifically address treatment, we have previously shown that the clinical entities approach can reliably classify individual patients with long-standing adductor-related groin pain,54 and that a large proportion of these patients will experience full recovery (79%) when a specific exercise programme is initiated.54 Treatment of the other clinical entities and different possible pathologies, including hip joint pathology, should be the main focus of future research within the field of long-standing hip and groin injuries. While arthroscopic procedures seem to be promising, with significant and large effect sizes,55 randomised studies are needed in this area, as surgery may be a very placebo-prone intervention.56 Ekstrand and Ringborg conducted a randomised controlled trial where patients with inguinal groin pain were allocated to inguinal surgery (sports hernia repair), individual training, physiotherapy or a control group. The patient who underwent inguinal surgery had significantly less pain throughout the follow-up period (3 and 6 months) compared to the other groups.57 While it was originally criticised for the surgical approach, also including ilioinguinal and iliohypogastric neurectomy, the approach and study design was in many ways ahead of its time compared to the general ‘sports hernia’ case series approach.10–15 Future randomised controlled clinical trials, looking at placebo-surgery, or comparing standardised conservative care, plus/minus surgery, are therefore important designs to consider in the future, to evaluate when surgery is indicated.

Football as an exceptional in vivo model for hip and groin injury

At the Arthroscopic Centre Amager, Copenhagen, hip and groin injuries have been a primary clinical focus during the last 15 years, and research activity has gradually increased. Our aim has been to address the most common clinical conditions and questions that we face when managing these injuries, including both treatment and preventive measures. Hip and groin injuries are frequently seen in many different sports, particularly in football and ice hockey.58–60 In elite football, it has been reported that 10% of all players suffer a new hip/groin injury each season.61 But regarding the prevalence of these conditions, it has been observed in recent studies that up to 70% of male soccer players experience hip and/or groin pain during one season,28 ,62 suggesting that previous incidence reports may only represent the tip of the hip and groin injury iceberg. Soccer is therefore, while discouraging for the athletes, a real-life model with exceptional possibilities to study both acute and overuse injuries in the hip and groin region. During the last 15 years, we have included more than 3000 soccer players in studies on hip and groin injury incidence, prevalence, clinical examination, physical assessment, management and prevention. One of the common clinical findings in many of these athletes is pain and weakness related to the hip adductors.22 ,28 Consistent evidence now exists that adductor weakness is not only associated with hip and groin injury,22 ,28 but also precedes and predicts injuries in this region.31 ,63 ,64 It is therefore important to address hip adductor weakness in many of these athletes. An important question to be answered in the future is which structural components, including nerves, muscles, tendons, bones or joints, this associated weakness is primarily related to.

Prevention preferred over cure

As many hip and groin injuries are long-standing in nature, the development of effective preventing strategies is of extreme importance, as this can reduce many days of injury and frustration for the athlete. We have previously demonstrated that a programme based on the adductor exercise treatment programme54 showed promise by a 30% numerical reduction of groin injuries in the prevention group65 when including approximately 1000 players. This potential reduction was, however, not statistically significant, as the study was powered to detect a 50% reduction, and with a 30% reduction we would have needed 5000 players.65 As the exercises in this groin injury prevention programme were based on experience and personal intuition concerning which exercises would be most beneficial, we have now changed our research strategy, so that specific exercises for possible future use in hip and groin injury prevention and treatment are now being systematically and quantitatively evaluated. These investigations include neuromuscular activity/intensity profile during specific exercises (electromyographic activity and activation-levels),66 relevant contraction-specific strength improvements (dynamometry), such as increased isometric and eccentric strength,67 ,68 perceived exertion (Borg scale), delayed onset muscle soreness (numeric rating scale) and possible side effects associated with these exercises.66–68 The purpose of this is to introduce a more targeted scientific approach when introducing exercises for primary or secondary prevention in the future. This will hopefully induce a larger effect, such as seen previously with a targeted eccentric strengthening programme for preventing hamstring injuries, based on a clear scientific rationale, which substantially decreased the injury rate by 70%.69

From eminence to evidence

By including reliable and valid clinical tests and outcome measures in future research, comparison of valid data and outcome from different studies, concerning athletes with hip and groin injury, becomes possible. With these new and important advances, we hope that the general clinical research approach within this area will change from primarily descriptive case series to experimental designs, such as randomised controlled trials. To get a better understanding of the complex hip and groin pathology and anatomy, an increased focus on basic and clinical experimental research and their relation is needed in the future. We therefore advocate using more rigorous scientific approaches, concerning hip and groin injuries, to advance this important area of sports medicine, from being eminence-based to becoming evidence-based.