Sports Medicine: Just the Facts

REMODELINGSTAG E

• Healing bone is restored to its original shape, struc-
  ture, and mechanical strength.


• Remodeling is a long-term process facilitated by
  mechanical stresses placed on the bone.
  a. Axial loading across the fracture site leads to bone
  being deposited where it is needed and reabsorbed
  where it is not (Wolff, 1986). Adequate strength is
  typically achieved in three to six months.

BIOMECHANICS OF FRACTURES

STRESSFRACTURES(WHITE, PANJABI,
ANDSOUTHWICK, 1977)

• Cyclic loading repeated over a long period of time
  may cause disruption of the bony architecture.


• The susceptibility of bone to fracture under stresses of
  low magnitude is related to its crystal structure and
  collagen orientation.


• Under each cycle of loading, a small amount of
  strained energy may be lost through microscopic
  cracks along the cement lines of bone.
  •Fatigue load under certain strain rates can cause pro-
  gressive accumulation of micro damage in cortical
  bone.
  a. Prolonged loading may eventually lead to failure
  through propagation of these cracks.
  b. Bone may be created near the microscopic cracks
  through periosteal callus formation, thus arresting
  propagation.

ACUTEFRACTURES(BRIGHTON, 1984)

• Classified according to the magnitude and area of dis-
  tribution of the force applied and the rate at which the
  force acts.
  a. Soft tissue injury and fracture comminution
  directly proportional to the loading rate (Karladani
  et al, 2001).
  b. Modifies normal healing response by changing
  concentration of normal reparative mediators.
  •Typically force is applied to bone in many directions
  and generates compressive, tensile, or sheer stress (or
  some combination).


• The combination of the bone’s material strength and
  anisometric properties dictate when, how, and along
  which path a fracture will occur.
  a. Cortical bone is generally weak in tension and shear.
  b. Area where tensile stresses arise fails first.
  •Transverse fractures are the result of pure tensile
  forces or bending.


• Fractures from pure tensile force occur progressively
  across the bone, creating a transverse break without
  comminution.
  
  
  • The pattern of fracture arising from pure bending is a
    simple tranverse line.
  
  
  • Bone undergoing rapid loading must absorb more
    energy than bone loaded at a slower rate.
    a. At low speed, bending with tensile stress will cause
    a fracture with a single butterfly fragment.
    b. High speed bending will cause several butterfly
    fragments.
  
  
  • The pattern of bone injury also impacts healing capac-
    ity (Carter, Blenman, and Beaupre, 1988).
    a. Time to union is greatly prolonged in fractures
    with more soft tissue stripping.
    b. Larger load under bending failure may cause the
    surrounding soft tissues and periosteum to sustain
    more damage and thus may affect the fracture heal-
    ing potential.
  
  
  
  

FACTORS INFLUENCING

FRACTURE REPAIR

NUTRITION

•Typical diet including all food groups in proper

amounts is enough to effect healing in a healthy indi-

vidual.

1. Calcium usage is limited by absorption.
   a. Preinjury calcium levels are predictive.
   b.Intake of about 1g/day is optimal, along with
   supplemental vitamin D up to 1000 IU/day.


2. True vegans with no alternative proteins risk for
   nonunion.

AUGMENTATION OF FRACTURE HEALING

(EINHORN, 1995)

OSTEOGENESIS

• Naturally occurring material to induce or support the
  formation of bone

CANCELLOUSGRAFTS

• Cancellous grafts effect vascular ingrowth and progen-
  itor mesenchymal cell invasion, osteoblastic apposi-
  tional new bone formation, and ultimately, remodeling
  of the trabecular structure.

CORTICALGRAFTS

• Slow to vascularize


• Must undergo osteoclastic resorption prior to oste-
  oblastic new bone formation


• Do not demonstrate complete incorporation


• Healing process begins at host–graft cortical junc-
  tion

64 SECTION 1 • GENERAL CONSIDERATIONS IN SPORTS MEDICINE