Discussion
The aim of the study was to describe the morphology of the hip joint in rowers and investigate the association of cam morphology with lumbar disc disease. A high prevalence of asymptomatic labral tears, cam morphology and lumbar disc disease was observed in elite rowers. Moreover, reduced internal rotation of the hip secondary to cam morphology may be associated with degenerative lumbar disease in elite rowers.
Hip joint morphology in rowers
There are very few studies that describe the morphology and characteristics of a rowers hip joint.6 21 Our study is the first detailed review of a cohort of elite rowers hips. We found 85% of rowers have unilateral cam morphology, 60% have bilateral involvement and 72.5% of all hips met the criteria for cam morphology. The prevalence shown in this study was comparable to elite ice hockey players,22 football players23 and American football players.24 The mean alpha angle of the hip joint was at its greatest at 1 o’clock for both bone and cartilage. The mean alpha angle was comparable to angles seen in a footballers16 23 25 elite ice hockey players22 but overall was higher compared with a general sporting population.26
MRI analysis revealed 95% of rowers in this cohort had at least one hip with a labral tear and 75% of all hips of the cohort had a labral tear. However, during their entire rowing career to date, only 50% of the cohort had experienced hip/groin pain in at least one hip and only 35% of all hips in the cohort had hip/groin pain. Similar to our study, other studies have shown that athletes are likely to have asymptomatic labral tears in 54% of hips.27 Only one rower having articular cartilage involvement is probably a reflection of a younger age group, where more advanced changes due to FAI has not developed as of yet.
The negative correlation between internal rotation, total rotation and hip extension and alpha angle of the hip joint is an important finding, as these are potentially simple bed side tests that can be performed to assess FAI. Especially the increasing alpha angle strongly correlated with reducing hip joint internal rotation, which consolidates findings of previous studies.16
Cam development is thought to be at its maximum at ages 12–14.16 The majority of our cohort did not start rowing until 14 years of age, hence the development of cam morphology likely preceded the introduction of rowing into their exercise regimen.
Rowers lumbar spine
It is well known that rowers experience episodes of lower back pain.28–30 The most common pathology driving this is possibly lumbar disc disease.31 In our cohort, almost all (95%) rowers had back pain at sometime in their career. The average Oswestry Disability Index was 4.7%, which suggests low disability within this cohort due to back pain. We found that radiological degenerative disc disease defined by Pfirrmann score was the most common disc pathology evident in our cohort. We found disc herniations (30% of total spines) and nerve root impingement (0%) a rarer finding, however, the limitation of having only a sagittal T2 image must be considered. Three rowers had bilateral spondylolysis and secondary spondylolisthesis. In all cases, spondylolisthesis was grade 1 changes.32 Spondylolysis was bilateral in each case and from T2-weighted images, there was no indication of these being active, however, we did not have STIR MRI images to be certain.
Hip joint morphology associations with the lumbar spine
Kinematic studies have identified increased lumbar-pelvic flexion as a contributing factor to lumbar back pain as a consequence of increased loading in the lower lumbar spine.33–35 Anterior rotation of the pelvis on the hips is key to the rowing stroke as, in conjunction with hip flexion, it enables the individual to achieve the technical component known as the catch.36 In the presence of cam and/or pincer morphology, it is hypothesised that one of two mechanisms occur: repeated hyperflexion of the hip joint during the rowing stroke may predispose to the development of chondrolabral pathology.6 Alternatively, to avoid premature contact between the proximal femur and acetabulum, the individual may posteriorly rotate the pelvis, leading to hyperflexion and increased loading of the lumbar spine.36 The relationship between increasing lumbopelvic flexion and asymmetrical hip flexion has previously been reported.37
In our study, the highest mean alpha angle was noted at 1 o’clock. For this we felt that this is the most likely area of the head/neck junction of the femur to first make contact and impinge with the labrum/acetabular rim during a rowing stroke. We used this alpha angle to correlate with a combined Pfirrmann score for the whole spine. The combined score has been used in previous studies to capture the degenerative disc disease within whole of the lumbar spine.19 There was a correlation seen between the alpha angle at 1 o’clock and the combined Pfirrmann score. Degenerative disc disease is the most common at L3/4, L4/5 and L5/S1 accounting for 70% of disc disease,38 this was also the case in our cohort, and we found that a combined score for these discs again correlated with hip joint alpha angle. Furthermore internal rotation of the hip joint negatively correlated with the size of the alpha angle and also both combined Pfirrmann scores. These findings suggest that the hip morphology and reducing hip internal rotation may have an association with lumbar disc disease. This is a unique finding in a cohort of elite rowers.
More recently, it is recognised by senior clinicians working in elite rowing that hip morphology may play a part in the development of back pain in rowers. It is also possible that abnormal spinal movements and lower back pain could be the first signs of coexisting hip joint impingement in this population. Our study is the first study to show this radiological association.
Impact on clinical practice and wider population
Our findings suggest that FAI and lumbar disc pathology are likely linked. The role of FAI in the development of lumbar spine pathology is largely unknown. We propose that when an elite athlete presents with back pain they should have their hip, pelvis and lumbar spine assessed with a focus on potentially adverse effects of FAI on lumbopelvic movements.
The negative correlation between hip joint internal rotation, and disc degeneration is a novel finding. Such a finding may give the clinician a simple bedside test to screen at risk populations.
From previous studies, we know that hip joint FAI changes are prevalent in the general population.39 Furthermore, back pain due to lumbar disc disease is one of the most common musculoskeletal problems in the general population.40 This certainly raises the possibility that FAI morphology plays a significant part in causing degenerative lumbar disc issues than earlier thought. This is the first such study that has looked at this, and next stages from this exploratory study would be to look at a larger cohort of subjects.
Limitations
The main limitation in this study is its sample size. We must stress that this is an exploratory study and would make way for a larger study looking at this association further. We appreciate that most lumbar degenerative disk disease are asymptomatic.41 However, in this exploratory study, it was aimed to show that there was merely a radiological correlation between FAI and a measurable radiological pathology (degenerative disk disease). Furthermore as 95% of our cohort had back pain at some point in their life it was not possible to draw conclusions regarding the associations between back pain and hip morphology.
To examine the lumbar spine, we only used one MRI sequence. While this was sufficient to grade degenerative disc disease using the Pfirrmann score, it was difficult to review pars defects, subtle neural compressions and modic changes in detail. Further limitations apply to using the alpha angle as a morphological measure. There exists no universally agreed diagnostic threshold for cam morphology and a quantitative value for pathological change in alpha angle is unknown.42