Diagnosing Pain Generators throughout the Hip Using the Layer Concept

Last week, I gave a very brief introduction to the layer concept in my post Hip Impingement and the Unraveling of Related Diagnoses. I promised you I would dig deeper. Now I have. This post will probably be by far the longest post I will write. In fact, it deserves a book chapter.

The layer concept for diagnosing hip was developed by Dr. Bryan Kelly of Hospital for Specialty Surgery in New York, NY. It is quite fascinating how he details four layers of diagnosis and treatment. I wish every hip patient would get this kind of evaluation. Unfortunately, that’s not the case. But, by educating ourselves, identifying and finding the care we need, many of us might get closer to the Layer Concept and the Hip Center model that Dr. Kelly advocates (see aforementioned blog post).

The article I will be referring to is a complex piece that I will do my best to explain on a FIFTH layer of patient-friendliness. Dr. Kelly starts off by saying that it is crucial to decipher the cause of a condition versus the pain generator find the proper treatment. That may seem like a no-brainer. But if it was a no-brainer to every doctor I don’t think we would see The Layer Concept laid out in writing. He states that The Layer Concept was developed to provide a systematic way of going about diagnosing hip pathology and pain. During the diagnostic process, it may be helpful to categorize the hip as structurally normal, structurally overcovered or undercovered.

Structurally normal means that all the values fall within a normal range (center edge angle, hip valgus and hip version values). The undercovered hip presents with anteversion (femoral neck leans forward compared to the rest of the femur), hip valgus (shaft of femur is bent outward in relation to the neck of the femur) or dysplastic characteristics (shallow hip socket to varying degrees). The overcovered hip can  present with a CAM lesion at the neck-head junction of the femur, rim lesion (pincer), often associated with acetabular retroversion (hip socket “mouth” faces more to back and side than in normal hip), acetabular profunda or protrusio.

Now, I want to go over the four layers for basic understanding of what they entail.

Layer 1: Bone (the osseous layer)

Layer 1 consists of the femur (thigh bone), pelvis and acetabulum (hip socket). Structural problems may exist in this layer, which can be divided into developmental and dynamic pathologies. Developmental pathologies include dysplasia, femoral version, acetabular version, femoral inclination and acetabular profunda/protrusio. Dynamic related pathologies include CAM and pincer impingement  and delamination (cartilage peeling off bone).

CAM impingement can lead to labral tears and delamination of the hip socket at the contact site of the joint cartilage. CAM and pincer or both in combination are the most common. In Kelly’s paper other types of impingement (much less common) are also mentioned once you look closely at the paper's specific tests, for example, ischiofemoral impingement, trochanteric impingement and sub-spine (AIIS) impingement (will blog more about these separately, later).

Layer 2: Inert layer (tissues that cannot contract)

Layer 2 consists of the labrum, hip capsule, ligaments about the hip and ligamentum teres. The most important function of these tissues is to provide static stability to the hip joint. The labrum is the most commonly affected part of this layer, but ligamentum teres tears, capsular instability, ligament tears and adhesions of the hip capsule may also exist.

A relationship exists between Layer 1 and Layer 2. Cadaver studies have shown that cutting a hole in the capsule and creating a labral tear, causes the labrum to lose its suction seal which then, in turn, further stresses inert (and muscle) tissues.

Layer 3: Muscles

Layer 3 consists of all tissues that are able to contract, i.e. muscles. Such muscles support, control and create movement about the hip joint. They include muscles crossing the hip as well as lumbosacral (trunk stabilizers) and pelvic floor muscles. A number of pathologies of the muscles outside the hip joint may be directly related to underlying structural problems of the hip joint itself. For example, psoas may be impinged and snapping over the femoral head or the iliopectineal eminence (ridge on hip marking the junction of the ilium and pubis bones).

In addition, affected muscles may be the hamstrings at the ischial tuberosity (sitting bone), rectus abdominis (six-pack muscle), conjoin tendon and adductor longus. The injuries can different in nature: acute, traumatic or from overuse (tendinosis) and avulsions (tearing off bone). Interestingly, in studies when FAI patients were tested for their voluntary contraction levels (how much you are willing to contract your muscles without anyone or anything putting extra force on you), those levels were quite reduced for hip adduction, flexion, external rotation and abduction (compared to a control group). The TFL muscle also showed decreased activation during hip flexion in hips with FAI. Muscle injuries and deficiencies like the ones described are compensatory responses to Layer 1 and 2 pathologies.

For Layer 3 it is also noted that the adductor longus may act as a stabilizer when the abductor(s) is/are weak. The adductor muscles group is consistently found to be overactive in patients with hip joint pathology. Often the abdominal wall muscles are affected because of how they attach to the pelvis. Some research has noted clinical correlation between FAI and sports hernias (athletic pubalgia).

Dr. Kelly also mentions Dr. Janda’s work (Czech physician 1928-2002). Dr. Janda developed concepts of muscle testing, muscle imbalances and pain syndromes of the locomotor system. Dr. Kelly refers to Janda’s Lower Crossed Syndrome, postural adaptive changes, and that these must be considered when examining Layer 3. In the Lower Crossed Syndrome the abdominal and gluteal muscle groups are weak and inhibited whereas the rectus femoris, iliopsoas (both hip flexors) and thoracolumbar extensors (sometimes called paraspinals or erector spinae) are overactive and facilitated. When investigating Layer 3, it is also important to examine the effect of spinal pathology and the spinal nerves’ response to the muscle groups they innervate.

Layer 4: Neuro-mechanical

The fourth layer is a theoretical, neuro-mechanical, layer consisting of anatomical structure, physiological events and motion (kinematic) changes which drive awareness of movement and space (proprioception) and pain within the hip.

Locally, at the site of the hip, this layer refers to nerves and blood vessels (neuro-vascular), responses to touch, tension and pressure (mechanoreceptors) as well as pain responses (nociceptors). On a larger scale, Layer 4 refers to posture and position of the pelvis over the femur. The position of the pelvis may be affected by lumbar pathology resulting in torsion of the sacrum, rotation of the left or right half of the pelvis (innominate) or spinal motor nerve changes. Foot and ankle mechanics and the response of the lower extremity up to the hip also affect the position and posture of the pelvis over the femur. In addition, Layer 4 involves looking at functional movement patters, examining how motor learning affects dynamic movement of the pelvis over the femur or the femur under the pelvis.

Dr. Kelly talks about the different types of nerve endings. Without going into great detail of the nerves, it might be interesting to know that Type 4 – free nerve endings – found in the joint capsule, ligaments, tendons, blood vessels and fat pads are responsible for pain (nociceptive). Based on older study findings, Dr. Kelly states that the lack of motion and spatial awareness (proprioceptive mechanoreceptors) in the hip makes the hip more prone to neuromuscular inhibition and dysfunction than other peripheral joints.

Kelly cites another study to show that neuromuscular and reflexive relationships as well as chains of adaptive reactions alter movement patterns throughout the body. He argues that if an ankle injury can cause a change in muscle firing patterns at the hip, then low back or hip pathology affecting muscle function at the pelvis can also change the mechanics from the trunk down and impact how the foot hits the ground.

Injury at L5-S1 can cause inhibition of segmental stabilizers (muscles that align bones), multifidus (spine/core stabilizer) and transverse abdominis (deep core stabilizer). The distribution of the L5-S1 nerve roots affects the hip abductors, hip external rotators, hip extensors, knee flexors, peroneals, dorsiflexors and plantar flexors.

Dr. Kelly states that understanding the neuromuscular relationship of spine and lower quarter is imperative to successful examination and treatment of hip patients. Layer 4 also involves testing for various nerve entrapments and pain syndromes.

Now that I have explained what the four layers entail, it is time to look at the treatment by layer.

Treatment by Layer

According to Dr. Kelly it is not unusual to need a few visits to diagnose and decide upon a treatment plan. Immediate conclusions are hard to draw since it is important to understand the compensatory movement patterns and femoral and pelvic mechanics. The screening process starts from Layer 4 with a functional movement exam and spine assessment whereas the clinical hip exam begins from Layer 1 and moves out toward Layer 3. A series of special tests is used for the different layers.

Treatment (I take it conservative treatment or hip surgery rehabilitation) begins from Layer 4 and progresses in toward Layer 1. It starts in Layer 4 with by addressing the motion chain if there is a dysfunction. Dr. Kelly states that it is of utmost importance to recognize a restriction, hypermobility (lax ligaments leading to excessive joint mobility) or pelvic obliquity (pelvic tilt in relation to spine) or torsion of the sacrum (rotation of sacrum about an oblique axis) when examining the spine; the effect on muscle imbalance or nerve-muscle dysfunction will significantly affect the joint movement and muscle timing around the hip. It is imperative to address restrictions of the spine and/or pelvic obliquity by means of manual therapy techniques prior to attempting to re-educate muscle function. It is equally important to address how the foot hits the ground and its effect on the hip and pelvis.

For treatment of Layer 3, the soft tissue and fascia, the practitioner needs to evaluate the restrictions, tightness and tone of the soft tissue. Neuromuscular re-education is not effective if these factors are not first addressed. Dr. Kelly explains that muscle tone must be distinguished from muscle tightness and that the two are not the same. Muscle tightness shows a palpable restriction at the end range of tissue length or there is resistance to movement of the tissue throughout its length.

Tone, on the other hand, may be caused by a spinal pathology, which is why tone needs to be clinically correlated to findings from examining Layer 4. Tone can also be protective. Dr. Kelly refers to the adductors to explain protective muscle tone. When there is pain in the hip and inhibition of primary hip stabilizers, as so common in FAI patients, it makes sense that the adductors would respond to assist in protection and stabilization.

So how does the treatment vary between muscle tightness and tone? Soft tissue mobilization and static stretching may be effective for a tight or shortened muscle. BUT, soft tissue mobilization alone will not be effective for a muscle with tone. A muscle with tone needs to be neuromuscular inhibited and then re-educated in proper timing and functional sequence patterns. Stay on the lookout for my next blog post where I will be blogging about neurokinetic therapy and its potential role in hip rehabilitation.

Dr. Kelly states that re-education of these core and hip stabilizers has most successfully been achieved in an unloaded position (my interpretation: in prone or side-lying) to later progress to an upright loaded position.

In treating the inert tissues of Layer 2, Dr. Kelly notes that these tissues can be addressed through joint mobilization ONLY after all soft tissue restrictions have been addressed. He states that joint capsules treated with mobilization without definitive clinical reasoning may be detrimental to the recovery process. In other words, if your hip has normal mobility of the capsule but a restriction of the fascia, the restriction of the fascia must not be overlooked and replaced with joint mobilization because the hip may become unstable, causing more pain and pathology.

Once your hip is mobilized and you gain new motion the muscles need to be taught to function through the new range. If your hip capsule is hypermobile (lax ligaments) or the ligamentum teres has been disrupted, Dr. Kelly explains that it is still necessary to work through all of the soft tissue restrictions. After that has been done, you can slowly start developing a balanced, dynamic muscular stabilizing structure around the core and hip.

According to Dr. Kelly, treatment of Layer 1 – bones – is the most difficult in the rehabilitation setting. I’m not sure what he means by this. Maybe that you cannot actually rehabilitate bone…The bony abnormalities, whether CAM, pincer AIIS or trochanteric impingement, would be treated by surgery. Once you rehab from surgery, treatment by layer makes a lot of sense. Or, alternatively, if you try a conservative approach to potentially avoid surgery. Labral tears may actually be become asymptomatic if appropriate physical therapy is prescribed and performed (this piece of information comes from Dr. Kelly’s website). But bony abnormalities do not disappear. Symptoms of Layer 1 may be alleviated by avoiding deep flexion, adjusting your car seat or desk chair as well as modifying your exercise.

Dr. Kelly concludes that hip rehabilitation is not linear. Dysfunctions may exist across Layers 1 through 4, making treatment challenging. The forces placed on the hip, the number of muscles crossing the joint and the multitude of anatomical layers under load, require a systematic and advanced clinical approach (reasoning) to diagnosis and treatment. Kelly cautions that results can be remarkable when proper treatment is prescribed, but devastating when surgery was performed for the wrong reasons.

The referenced paper by Dr. Kelly is a wonderfully structured document and concept. I hope by introducing it to you, my readers, that you will go “armed” to their appointments, whether with physical therapists or doctors. It doesn't matter whether you are in the post-surgical rehab stage or in the process of finding a diagnosis. Read, learn and ask all the questions you want. You deserve to know the answers.

So does my heavy emphasis on one single paper mean that Dr. Kelly is always right? Maybe not, but he does see a lot of patients, including high level athletes and does perform a ton of research. I certainly give a high credence to his thought process and the sixty sources of this paper. As always, use your own judgment and provide your doctors with the clues that your body gives you.

Source: Curr Rev Musculoskelet Med (2012) 5:1-8. The layer concept: utilization in determining the pain generators, pathology and how structure determines treatment. Peter Draovitch, Jaime Edelstein, Bryan T. Kelly.