Bio Mechanics


by George J. Davies, PT, ATC, and Todd S. Ellenbecker, PT

Focused exercise aids
shoulder hypomobility



Limited range of motion (ROM) of the shoulder complex is one of the more common conditions seen in the clinical setting. Often these impairments lead to pain, compensations (with resultant pain and prob- lems occurring elsewhere in the kinetic chain), limited ability to perform various activities, and limitations of functional performance. The hypomobile conditions that create the limited ROM and impairments present a formidable challenge to the clinician. About 23% of visits to family-practice physi- cians are for musculoskeletal problems.1 A 1993 review article2 reported that in Canada, less than 3% of preclinical medical school curriculum is devoted to musculoskeletal topics and only 12% of medical schools mandate clinical training in musculoskeletal medicine. In a survey3 of prima- ry-care pediatric residency graduates, sports med- icine/orthopedics was one of two areas in which graduates felt weakest. The latest piece of evi- dence is a recent report by Freedman and Bernstein4 published in the Journal of Bone and Joint Surgery. The authors administered a validat- ed musculoskeletal knowledge examination to 85 new residents at the University of Pennsylvania in Philadelphia. Seventy (82%) of the 85 residents failed.
Selective hypomobilites The reason we begin with these comments is that often when patients who have some pain and limited range of motion are seen by general physicians, they are diag- nosed with frozen shoul- der syndrome. Frozen shoulder syndrome (or adhesive capsulitis) has
been reported to go through a natural history of freezing, frozen, and thawing stages, which take many months to resolve.5,6 We think that more often, problems with decreased ROM are due to selective hypomobilities. These selective hypomobilities can involve the joint capsule/ligaments (noncontractile tissue) or the musculotendinous unit (contractile unit). Harryman et al7 have described the reaction of the joint when the joint capsule becomes asymmetrically tight. Karduna et al8 measured humeral head translations with active and pas- sive glenohumeral joint internal and external rotation. They reported posterior humeral head translation with external rota- tion and anterior humeral head translation with internal rota- tion. These studies8,9 report glenohumeral joint arthrokinemat- ics that represent a departure from the traditional ball and socket movements of a convex humeral head moving on a con- cave glenoid fossa.10 Instead, the arthrokinematics create an obligate translation of the humeral head on the glenoid fossa; these occur with active and passive range of motion. In a selec- tive hypomobility of the capsule, asymmetrical tightening of the capsule causes an obligate translation away from the side of the joint where there is a tight capsular constraint mechanism. One common example specific to the glenohumeral joint is in the patient who presents with posterior capsular tightness. Harryman et al7 has demonstrated that with a cross-arm adduc- tion movement, an increase in anterior humeral head transla- tion existed in cadaveric shoulders with experimentally created posterior capsular tightness. Additionally, with forward flexion, increased superior migration of the humeral head was present with asymmetric capsular tightness. These biomechanical prin- ciples will help determine part of the approach to be used dur- ing mobilization treatments. Examination The first challenge is to perform a comprehensive evaluation to determine the cause of the underlying hypomobility. 11 Such passive movement testing as the load and shift test7,9,12 and sulcus sign test9,13 are used to assess humeral head translation, edge loading responses, and capsular end feels.14 Although these tests are designed to assess translation or laxity, if the translation is limited due to a capsular end feel, it seems appropriate to assume that the capsule is hypomobile. Obviously, bilateral testing should be per- formed. Additionally, clinical experience helps differentiate the normal from the abnormal. This concept has been further dis- cussed recently by Davies et al. Range-of-motion measurements are done to assess the internal and external rotation of the shoulder. We think it is important to use an isolated measurement of glenohumeral joint internal rota- tion as well as a composite measurement of the glenohumeral and scapulothoracic movements.15 The close association between internal rotation of the glenohumeral joint and posterior shoulder tightness has been demonstrated in a new side-lying clinical mea- sure in patients with glenohumeral joint impingement and in throwing athletes.16 The integration, elaboration, interpretation, and clinical application of these concepts of shoulder complex hypomobility are described in the previously mentioned com- mentary.15 Soft tissue mechanics Adverse reactions to prolonged immobilization include scar tissue accumulation and a soft tissue contracture. This alteration in soft tissue leads to decreases in range of motion and arthrofibrosis. These alterations in the collagen and fascial tissue occur at the microscopic level. Intermolecular and intramolecular cross-links form in the periarticular connective tissue, which cause shorten- ing, resultant contractures, and the development of adhesions.17-20 Treating soft tissue contractures The primary rationale supporting the use of stretching exercises for increasing ROM is the biological principle that periarticular connective tissue will remodel over time, in response to the type and amount of physical stress the tissue undergoes. An objective of the stretching regimen is to get the collagen fibers to become oriented parallel to the lines of stress that increase ROM, as well as tensile strength. Parallel fibers assist in increasing ROM and normalizing the soft tissue. This process of soft tissue remodel- ing along the lines of stress is called Davis’s law of soft tissue remod- eling, and is analogous to Wolfe’s law of bone remodeling. The remodeling process is a biological phenomenon that occurs over long periods of time rather than a mechanically induced change that occurs within minutes. This is one reason joint mobi- lizations by themselves are not effective in increasing ROM around joints with significant contractures and arthrofibrosis.21 Following trauma, scar tissue formation is influenced by mechanical stress. This scar tissue becomes less amenable to change over time. Consequently, the sooner treatment interven- tions are applied, the more likely the tissue will respond. Decreased intervals of time between the onset of symptoms and the initiation of treatment has been one influencing variable reported in the treatment of the stiff and painful shoulder.21 Soft tissue deformation The stress-strain curve demonstrates the tissues’ response to treat- ment techniques.22-27 When tissue is treated longer or with more stress, the tissue deforms more. When treatment is applied for too short a time or without enough force to create a significant change in the tissue length, an elastic deformation response occurs. This is analogous to taking the “crimp” out of the colla- gen and is also known as “toe deformation.”This imperfect response of the tissue leads to little resultant gain in ROM. The desired result of treatment is to create a permanent change in the collagen tissue of a kind called plastic deformation. This occurs when there is microtrauma at the cellular level breaking the cross-links of the periarticular connective tissue (which form between the collagen bundles and create the motion limitations) and elongating the actual collagen bundles. The collagen then needs to be stretched along the lines of stress to produce collagen realignment (soft tissue law of collagen remodeling—Davis’s law) and allow for collagen remodeling.
Treatment procedure Scientific data demonstrate that soft tissue elongation can be effected by heat, force, time, and cooling.22-28 The treatment pro- cedures that we currently use to address this are: • Patient performs an active warm-up. This produces a meta- bolic “inside” warm-up, which is the most effective way to heat up collagen tissue.29 Collagen deforms more readily when it is warmed up. The warm-up can be achieved using an upper body ergometer, a rowing machine, the handles on a Nordic Track machine, or through rowing and bench pressing motions with surgical tubing or Therabands. The warm-up should continue for 10 minutes using activities that specifically target the involved area. • A passive warm-up is then carried out using such physical therapy modalities as heating the involved area while it is in a stretched position to try to create plastic deformation of the col- lagen tissue. • The “TERT formula” (TERT = total end range time), is used to create this plastic deformation.28This prescriptive formula is based on intensity x duration x frequency. Intensity is the maximum stretch intensity the patient can tolerate based on his/her pain threshold, an example of a desired TERT duration would be 20 minutes with the tissue in a stretched position, and frequency should be three times per day. The optimum total TERT time should be 60 minutes per day. The first and second TERTs can usually be per- formed by the passive warm-up at the start of the treatment program and by stretching again at the completion of the treatment. The third TERT can be completed by the patient at home. • If we have additional concerns that the contractile unit (musculotendinous unit) is involved as a limiting factor, then we also use static positional stretching and/or PNF contract-relax. Research by Tabary et al30,31 has demonstrated that when the mus- cles are maintained in a shortened position, along with the non- contractile tissue, the (musculotendinous unit actually loses sar- comeres. Through stretching, these sarcomeres can be replaced. Based on recent research by Bandy et al32-34 the static positional stretches should be held for 30 seconds. At this point, manual therapy techniques, mobilizations, myofascial techniques, strain-counterstrain techniques, myother- apy, etc. should be done. The key to the success of this treatment approach is to gain neuromuscular dynamic control over the newly gained range of motion. How often have clinicians worked with patients to gain passive range of motion during a treatment session, only to have the patient return for the next follow-up visit having lost this pas- sive range of motion? Why does this happen? We feel this is main- ly due to the patient’s inability to gain control of the motion. Passive range of motion by itself in a joint, without dynamic con- trol, is useless. It is not functional ROM, and may in fact, make the patient vulnerable to injury. Gaining neuromuscular dynamic control is not accomplished just by having the patient use full ROM exercises in the rehabilita- tion program. Instead, application of multiple-angle isometrics or short arc exercises in the newly gained ROM should be performed. If the therapist has the patient exercise through the entire ROM, the patient will fatigue the muscles by the time they reach the end of the newly gained ROM. Additionally, full range-of-motion resistive exercises may result in recruitment of adjoining muscles in the kinetic chain or compensatory movements that are counter- productive and may ingrain abnormal, inappropriate movement patterns. Since the position over which the patient needs to gain functional control is often near end-ROM, the biomechanics of the joint and the length-tension ratio of the muscles are usually in a disadvantaged position. This further contributes to fatigue. Total leg/total body strengthening When throwing a baseball, about 60% of the velocity imparted to the ball actually comes from the legs and trunk. Consequently, when rehabilitating the “shoulder complex,” practitioners must rehabili- tate the entire kinetic chain. Working on the entire kinetic chain including core (trunk) stabilization, scapulothoracic, and distal arm strengthening are important in developing total arm strength. Application of cryotherapy to the involved tissue area in a maximally tolerated stretched position for 20 minutes encour- ages the collagen to contract (not shorten) in the elongated posi- tion.25 This second TERT helps create the plastic deformation response and help realign and remodel the collagen tissue.28 The patient then needs to perform the third TERT in the home exercise program to create the plastic deformation of the collagen and stretch out the arthrofibrosis. This can also be accomplished by the use of continuous passive movement (CPM), splinting, or casting. An integrated approach to examination and treatment tech- niques for patients who have selective hypomobilities, using both scientific and clinical rationale and outcomes research, is clearly indicated. There is excellent supportive research for some areas regarding the efficacy of treatment outcomes, whereas in other areas, rationale for the methods used is empirically based. 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