Happy birthday to BSEMS!
April marks 12 months since BSEMS opened its doors. Queenslanders have been through some pretty tumultuous times over this period, but have emerged stronger and more determined. Likewise, the BSEMS practice has grown and added to its core group of practitioners over this time. We are proud of our Multi-disciplinary clinic, and continue to aim to provide Brisbane and South East Queensland with a world class Sport and Exercise Medicine clinic. We are always open to suggestions as to how we can serve you better, so please feel free to leave your comments or thoughts.
This month’s blog topic covers throwing and overhead injuries. Whether you are a weekend warrior throwing around a park, or an elite athlete upper limb problems can result from the repeated action of throwing or using a racquet. Understanding the biomechanics of throwing helps you to appreciate the forces transmitted to the upper limb, and what problems can result from excessive use or poor technique.
Upper Limb Problems in Overhead Athletes
People of all ages are heeding the advice to become more active and participate in sport and recreation. So called ‘over head’ sports activities like throwing and racquet sports for the most part are simple, and require no special training to participate. However tremendous forces are placed though the upper limb during these activities, resulting in a combination of acute, and more commonly over-use injuries, that commonly present to General Practice. This article explains the biomechanics of common over head activities, which explains the forces placed on the upper limb, and subsequent injury development.
Throwing Biomechanics
Throwing is a ‘whole body activity’ that commences with drive from the large leg muscles and hip rotation and progresses through segmental trunk and shoulder girdle rotation. It continues with a ‘whip-like’ transfer of momentum through elbow extension and through the small muscles of the forearm and hand, transferring propulsive force to the ball. Movement of the trunk and contact with the ground allow for maximal transfer of energy to the ball. (Water polo players can throw at only half the velocity of baseball pitchers.) The forces transmitted to the shoulder are lower during serving in tennis as the racquet dissipates much of the impact force, allowing a greater intensity of serving compared with throwing.
Throwing can be divided into 4 phases.
1) Preparation and wind up:
The major forces arise in the lower half of the body and develop a forward moving ‘controlled fall’. The weight is shifted back on the ipsilateral leg and the body rotates so that the hip and shoulders are at 90º to the target. During this phase lasting 500-1000 milliseconds, the shoulder muscles are relatively inactive.
Problems in any part of the ‘kinetic chain’ (e.g. injured hamstring) could impact on the eventual position of the upper limb, and precipitate injury.
2) Cocking:
The shoulder moves into abduction through horizontal extension and then into maximal external rotation (ER). In this position, the shoulder is ‘loaded’ with the anterior capsule coiled tightly in the apprehension position, storing elastic energy, and the internal rotators (IR’s) are stretched.
Toward the end of cocking the anterior shoulder restraints (inferior glenohumeral ligament and capsule) are under the greatest strain- with repetition these structures can become attenuated leading to subtle instability.
The cocking phase, which also lasts 500-1000 milliseconds, ends with the planting of the lead leg, with the body positioned for energy transfer through the legs, trunk and arms to the ball. Together, the first two phases constitute 80% of throwing duration.
3) Acceleration:
This consists of the rapid release of two forces: the stored elastic force of the tightly bound capsular fibrous tissue, and forceful contraction from the internal rotator muscles.
This generates excessive forces at the shoulder articulation, and the cuff muscles are highly active to hold the humeral head into the socket. Muscle fatigue can lead to loss of coordinated rotator cuff motion and decreased support. There are enormous valgus forces placed on the elbow, which tends to lag behind the inwardly rotating shoulder. A large degree of torque present on the elbow joint causes shearing forces to the articular cartilage.
This phase lasts 50 milliseconds, 2% of the overall time. It concludes with ball release at approximately the ear level.
4) Deceleration/follow through:
Not all of the momentum is transferred to the ball and very high forces pull forward on the glenohumeral joint following ball release, with a distraction force of 80% of body weight. The forces that must be countered are: humeral IR, glenohumeral distraction and elbow extension. This places large stresses on the posterior shoulder structures and elbow flexors.
Both the intrinsic and extrinsic muscles fire at near their maximum, in an attempt to develop >500N to slow the arm down. The spine and its associated musculature have a significant role as a force attenuator. Toward the end of the throwing motion, the torso begins to rotate forward, thus acquiring some of the kinetic energy of the arm, helping reduce the burden on the shoulder stabilizers which are attempting to stabilize the scapula and hold the humeral head within the glenoid. This phase lasts 350 milliseconds (18% of the total time).
Changes in throwing arm with repeated throwing:
At the shoulder, long term throwing athletes have an increased range of ER, because of repeated stress to the anterior capsule in the cocking phase, and stretch or breakdown of the inferior glenohumeral ligaments. This may lead to anterior instability of the shoulder and secondary impingement. Throwers often have more lax shoulders than non-throwers.
The normal strength of IR: ER is approximately 3:2, but in throwers this is exaggerated and over time lack of ER strength may increase vulnerability to injury.
At the elbow, repeated valgus stress could lead to a breakdown of the medial stabilizing structures (collateral ligament, joint capsule, and flexor muscles). This leads to an increased carrying-angle at the elbow. Less frequently, there may be anterior capsular strains, posterior impingement, or forearm flexor strains and a subsequent fixed flexion deformity.
Injuries associated with overhead activities
Shoulder
Typically overhead athletes will complain of pain during the throwing action. Repeated throwing often results in impingement, which can be superior or posterior; apprehension or subtle instability (typically anterior); and over time wear and tear changes to the rotator cuff and/or labral cartilage.
Pain during the wind up and cocking phase may be associated with lax anterior restraints, subtle instability and over time cuff tendinopathy.
Pain during the acceleration phase may be due to an internal rotation deficit, tight posterior cuff and internal impingement. Over time this could be associated with the development of a SLAP (Superior labral anterior-to-posterior) lesion.
A thorough biomechanical assessment, including analysis of throwing action, can determine problems with shoulder mechanics, and allow a targeted rehabilitation process. Often weakness in the ‘stabilizing’ rotator cuff muscles needs to be improved, along with scapulohumeral dysrhythm. A Sports Physician is ideally suited to examine such patients and coordinate rehabilitation. Investigations like ultrasound or MRI are occasionally warranted, and rarely operative intervention will be indicated.
Elbow
The primary forces delivered to the elbow during throwing are a valgus and extension opening force. This produces:
- tensile stress to the medial compartment restraints (Ulnar collateral ligament, flexor-pronator mass, medial epicondyle apophysis, and ulnar nerve)
- shear stress to the posterior compartment (posteromedial tip of the olecranon and trochlea/olecranon fossa)
- compression stress produced laterally (radial head and capitellum).
Continued valgus and extension forces may produce olecranon tip osteophytes, loose bodies in the posterior or radio-capitellar compartment, and a kissing lesion (articular damage on the posteromedial trochlea caused by the olecranon osteophyte. Subtle laxity may cause excessive soft tissue stretch with flexor-pronator mass tendinopathy, and ulnar neuritis)
Treatment typically involves a period of avoidance of aggravating activities, correction of biomechanics, appropriate strengthening rehabilitation, and a graded return to the provocative activity, monitoring for a return of symptoms.
Problems specific to young athletes:
Younger athletes are especially vulnerable to over head over-use injuries. Whilst they are exposed to the same forces as adults, growth plates remain open and are susceptible to stress related injuries, and may lead to long term deformity.
Problems in the shoulder include:
Traction apophysitis at the attachments of deltoid and pectoralis major
Rotational bone stress or stress fractures in the humerus
Shoulder impingement
Problems at the elbow include:
Medial epicondyle apophysitis
Lateral compartment osteochondritis dissecans
Traction apophysitis at the triceps attachment to the olecranon
In the sport of baseball, strict regulations apply specific to age, regarding the types of pitch allowed, as well as the number of pitches and innings permitted. This has been effective in reducing ‘little league’ shoulder and elbow pain. Most other sports rely on common sense in relation to appropriate training load. Unfortunately in this day of elite sport and high training volume at a young age, unrestricted load often results in over-use injury.
Elbow pain in Racquet sports:
Elbow pain is common in racquet sports, and may be due to dominant activity of the wrist extensors. The impact between the ball and racquet produces a significant amount of force, and the ‘shock’ transmitted to the arm depends on how hard the swing is; the speed of the incoming ball; where on the racquet face the ball hits; the quality of the racquet; the string tension; and the stroke mechanics. The ‘sweet spot’ is the area on the tennis racquet where the initial shock is at a minimum- if the ball misses the sweet spot there is increased shock transmitted to the hand, wrist and elbow.
Tennis elbow or lateral epicondylosis, is an overuse tendinopathy of the common extensor origin. Golfers elbow is the same pathology at the common flexor origin. Ways to reduce the shock at impact include:
Lower the string tension
Increase the flexibility of the racquet
Increase the size of the racquet head
Increase the weight (lead tape to the head and handle)
Increase the grip size
Grip higher on the handle
A larger grip size prevents the player from gripping the handle too tightly. It is only necessary to squeeze firmly on the grip during the acceleration phase of the stroke. Over time an eccentric strengthening programme has been shown to improve strength and function, and reduce pain. Adjunctive treatments such as corticosteroid injection, autologous blood injection or shock wave lithotripsy may have a role in recalcitrant cases.
An understanding of the biomechanics of over head sports allows the astute physician to determine injury likelihood, accelerate diagnosis, and to commence appropriate treatment and rehabilitation.
Comments
Post has no comments.