Sports Medicine: Just the Facts

CHAPTER 44 • SHOULDER INSTABILITY 263

Potter HG, Weiland AJ, Schatz JA, et al: Posterolateral rotatory
instability of the elbow: Usefulness of MR imaging in diagno-
sis. Radiology204:185–189, 1997.
Rominger MB, Bernreuter WK, Kenney PJ, et al: MR Imaging of
anatomy and tears of wrist ligaments. Radiographics
13:1233–1246, 1993.
Shih C, Chang CY, Penn IW, et al: Chronically stressed wrists in
adolescent gymnasts: MR imaging appearance. Radiology
195:855–859, 1995.
Snyder SJ, Karzel RP, del Pizzo W, et al: SLAP lesions of the
shoulder. Arthroscopy6(4):274–279, 1990.
Sofka CM, Potter HG, Figgie M, et al: Magnetic resonance
imaging of total knee arthroplasty. Clin Orthop406:129–135,
2003.
Steinbach LS, Fritz RC, Tirman PFJ, et al: Magnetic resonance
imaging of the elbow. Eur J Radiol 25:223–241, 1997.
Stener B: Displacement of the ruptured ulnar collateral liga-
ment of the metacarpophalangeal joint of the thumb: A clin-
ical and anatomical study. J Bone Joint Surg Br 44:869,
1962.
Tartaglino LM, Flanders AE, Vinitski S, et al: Metallic artifacts
on MR images of the postoperative spine: Reduction with fast
spin–echo techniques. Radiology190:565–569, 1994.
Totterman SMS, Miller RJ: Scapholunate ligament: Normal MR
Appearance on three–dimensional gradient–recalled–echo
images. Radiology200:237–241, 1996.
Tung GA, Entzian D, Stern JB, et al: MR imaging and MR
arthrography of paraglenoid labral cysts. Am J Roentgen
174:1707–1715, 2000.
White LM, Kim JK, Mehta M, et al: Complications of total hip
arthroplasty: MR imaging—initial experience. Radiology
215:254–262, 2000.
Zanetti M, Jost B, Hodler J, et al: MR imaging after rotator cuff
repair: Full–thickness defects and bursitis–like subacromial
abnormalities in asymptomatic subjects. Skeletal Radiol
29:314–319, 2000.
Zlatkin MB: Techniques for MR imaging of joints in sports med-
icine. Magn Reson Imaging Clin N Am7(1):1–21, 1999.
Zlatkin MB, Iannotti JP, Roberts MC, et al: Rotator cuff tears:
Diagnostic performance of MR imaging. Radiology 172
(1):223–229, 1989.

44 SHOULDER INSTABILITY

Robert A Arciero

CLASSIFICATION

• Instability of the shoulder is a common problem.
  There is no report of incidence because of the large
  range in variability of presentation. There are three
  basic categories of instability. Instability should be
  considered as a spectrum of pathology: unidirectional

traumatic instability on one end of the spectrum,

acquired instability and atraumatic multidirectional

instability at the other end. (Thomas and Matsen,

1989)

A. TRAUMATIC

• Anterior: Fall with the arm in an abducted and exter-
  nally rotated position or an anterior force with the arm
  in abduction and external rotation (arm tackling in
  football, falling while snow skiing).


• Posterior: Posterior directed force with the arm for-
  ward elevated and adducted (MVA or pass blocking in
  football). Grand mal seizure or electrical shock can
  also produce a traumatic posterior dislocation.

B. ACQUIRED

• Microinstability: Subtle instability associated with
  pain in a throwing athlete or associated with rotator
  cuff tendinosis/dysfunction. This instability can occur
  from repetitive stretching of shoulder ligaments from
  activity or sports requirements.

C. ATRAUMATIC

•Multidirectional: These patients have symptomatic

glenohumeral subluxation or dislocations in more

than one direction. Many patients will present with

severe pain as an initial complaint and not overt insta-

bility. For treatment purposes it is important to differ-

entiate by patient history and physical examination

the primary direction of instability.

1. Primary Anterior: Pain associated with the arm in
   an abducted, externally rotated position


2. Primary Posterior: Pain with pushing open a heavy
   door


3. Primary Inferior: Pain associated with carrying
   heavy objects at the side

• Shoulder instability can be further classified:

1. Degree of Instability: Dislocation, subluxation,
   apprehension
   2.Chronology of Instability: Congenital, acute,
   chronic, recurrent


2. Direction of Instability: Anterior, posterior, infe-
   rior, superior


3. Laxity is not Instability: Laxity refers to translation
   of the humerus within the glenoid fossa. Many
   individuals are extremely lax but are asympto-
   matic. Instability refers to the symptomatic com-
   plaint of instability and dysfunction.