RemodellingExamples of remodelling (click here)
Fracture healing involves 3 phases
The remodelling phase lasts months and years after the fracture has healed. The healing callous is gradually resorbed and new bone laid down along the lines of stress. Rate of remodelling varies with:
SiteMetaphysis:The metaphysis serves as an active area of osteogenesis and remodeling in the development of normal bone growth. Diaphysis:The diaphysis is primarily an area in of relatively dormant osteogenesis. As a result there is less remodelling potential.
Process of remodelling
AngulationPhysis: In the skeletally immature individual, 75% of the angular remodelling takes place in the physis. The physis adjacent to a fracture tends to realign to become perpendicular to the forces acting through them by a process of asymmetrical growth. The concave side is stimulated to grow more rapidly to align the physis so as to become perpendicular to the long axis of the shaft of the bone. Once the physis is realigned, it then resumes symmetrical growth.
Roughly 20% of angular remodelling occurs in the diaphysis. Remodelling in the diaphysis follows Wolf's law. ie. Increased pressure (compression) on the concave side stimulates new bone formation. Tension on the convex side leads to resorbtion of bone. LengthFemoral fractureFracture healing stimulates bone growth in femoral fractures. Various lengths have been reported for femoral overgrowth following fractures 0.92 cm (range 0.4–2.7). Overgrowth in femoral fractures appears to be independent of:
The effect of growth stimulation may continue for three years following the fracture. Tibial fractureGrowth stimulation following fractures of the tibial shaft is age dependent. The maximum stimulation of 4.2 mm occurs in the 3–5 year age group. In older children stimulation is less with some actual growth inhibition as the child reaches maturity. There appears to be a greater tendency to increased tibial overgrowth in open fractures.
RotationFor practical purposes no rotational remodelling occurs.
Relationship to growth potentialUpper extremity:In the upper extremity, the proximal humeral and distal radial growth centres account for the majority of growth in the extremity. Thus, the remodelling potential in these areas is extensive. Fractures about the elbow, especially the distal humerus, have very little remodelling potential.
Lower extremity:The potential for remodelling in the lower extremity is less than in the upper extremity, most growth is around the knee and as such remodelling potential is greatest around the distal femur and proximal tibia (knee region).
The three major factors that have a bearing on the potential for
angular remodelling are:
Remodelling of specific fracturesThe remodelling capacity of fractures in the various parts of the upper and lower extremities varies considerably. Hand fracturesPhalanges:Very little remodelling can be expected in the fractures involving the distal portions (supracondylar and condylar areas) of the proximal and middle phalanges. In the proximal portions of these proximal and middle phalanges, some remodelling can be expected in the sagittal plane. Less can be expected in the coronal plane. Unfortunately, very little information is available in the literature as to the acceptable degrees of angulation for phalangeal fractures in children.
Metacarpals:Controversy centres on the acceptable angulation of volarly angulated fractures of the fourth and fifth metacarpal necks. Some are very liberal in their manipulative indications, accepting up to only 35–40° of volar angulation. Others are very conservative and have found that the ultimate function with those fractures that are not manipulated is equal to those that were. The only difference in those that were not manipulated was the absence of the prominence of the metacarpal head (knuckle).
Summary of the expected degrees of remodelling of the various fractures of the bones of the hand
Distal radial fracturesDistal radial physeal fractures:This area has probably one of the greatest potentials for remodelling of any fracture in the immature skeleton. Aitken showed that up to 50% displacement of the fracture fragments can be expected to remodel fully if there is at least one and a half years of growth remaining.
Distal radial metaphyseal fractures:Have a great potential for angular remodelling. The commonly accepted angulation that will fully remodel with five years of growth remaining is 30-35° in the sagittal plane and 10° in the coronal plane. In many cases, however, the remodelling angulation may not be complete but there is no functional or cosmetic residual. Bayonet apposition can be expected to
remodel in patients up to 12 years
as long as the linear alignment is nearly anatomical. Reduction necessary? In a recent by Do et al it was felt that the degree of remodelling in this area was so great that the majority of their distal radial metaphyseal fractures did not even require a primary reduction. They accepted up to 15° of primary angulation and 1 cm of shortening in boys up to 14 years of age and girls up to 12 years of age. Their opinion was that it was a waste of time and financial resources to manipulate displaced fractures meeting these criteria. It was their observation that even those fractures that were completely unreduced had essentially complete remodelling at the termination of their growth.
As a rule of thumb if the deformity is clinically visible manipulation is indicated.
Radial and ulnar shaft fracturesAcceptable malalignment of the radial and ulnar shaft depends on multiple factors. Price has set down some guidelines for the various factors involved. He also found that impingement across the interosseous space by the fracture fragment was an unpredictable factor in determining the ultimate outcome.
Plastic deformation: Vorlat and De Boeck, found that over the age of six years, more than 10° of plastic deformation of either the radial or ulnar shafts would result in an unacceptable result.
Radial neck fracturesDepends on degree of:
Angulation: There is not a total consensus on the amount of angulation of a radial neck fracture that can be accepted with resultant satisfactory remodeling. The most commonly accepted number is 30° of angulation. However, other studies have demonstrated that even those with up to 50° of angulation can be expected to achieve good results.
Translocation: Originally, it was felt that as little as 2 mm of translocation results in a poor outcome. However, more recent studies have shown that up to 5 mm of translocation will remodel.
Clinical examination: Probably the best method of
determining what degree of deformity will result in
an acceptable outcome involves a clinical examination
under sedation or anaesthesia to determine the passive range of forearm motion.
If there is at least 50° of supination and 50° of pronation, the patient should
be expected to have a satisfactory functional result. Supracondylar humeral fracturesAngulation—no: Very little angulation in the sagittal plane can be expected to remodel. Up to loss of 20° of the shaft-condylar angle can be tolerated. This usually only manifests as a lack of full elbow flexion with some increase in elbow hyperextension. In the coronal plane, no angular remodeling can be expected. Angulation into varus will result in an unacceptable cosmetic deformity. It has also been shown that cubitus varus produces some functional effects such as recurrent fractures of the lateral humeral condyle or late ulnar nerve neuropathy.
Translocation—yes: Translocation of as much as 100% in either plane has been shown to demonstrate complete remodeling.
Humeral shaft fracturesThe humeral shaft has considerable remodeling potential, especially in the very young. Kwon and Sarwark reviewed the literature and come up with some guidelines as to acceptable displacement, see table below:
Fortunately, minimal angulation is well hidden by the muscles of the arm.
Proximal humeral fracturesProximal physeal injuries: Fractures through the proximal humeral physis tend to develop significant angular deformities because the rotator cuff muscles are acting only on the proximal fragment. The opposing shoulder girdle muscles are acting only on the distal fragment. Fortunately, however, because of the marked flexibility and circumduction nature of the shoulder, a residual deformity can produce an acceptable cosmetic and functional result in most children. In those patients that use their upper extremities for high performance athletic activities however, anything less than an anatomic reduction however may result in some loss of athletic performance. Thus, the expected future function of the child’s extremity and not the degree of displacement may be the primary consideration in determining the aggressiveness of the treatment.
Beaty has set out guidelines for each age group.
Proximal metaphyseal injuries: With this fracture pattern there is some resistance to external rotation and abduction of the proximal fragment because of the persistence of muscle insertion of the pectoralis major on the proximal fragment. Thus many of these fractures if complete, tend to present with bayonet apposition. By and large this bayonet apposition can be expected to remodel to a satisfactory degree if there is at least 2 years of growth remaining.
Femoral shaft fracturesAngular malalignment: Malalignment in both sagittal and coronal planes is somewhat age dependent. Kasser outlined his recommendations for acceptable angulation in the various planes as it relates to the specific age groups.
Because of the normal natural anterior bow of the femur, more angulation can be tolerated in the sagittal plane.
Shortening: The amount of shortening expected to correct has been discussed previously in the section on femoral overgrowth. It must be remembered that a combination of angulation with shortening has an additive effect and can spell trouble regarding an acceptable outcome.
Loss of rotation: Davids has shown that rotation does not significantly remodel. He did find in his studies that up to 25° can be well tolerated.
Tibial shaft fracturesAngular malalignment: The tibia is very unforgiving in its ability to remodel. This may be because it is composed of a very large amount of diaphyseal bone. Remodeling in the sagittal plane is better than in the coronal plane. Varus has a better chance of remodeling than valgus. Heinrich has set out guidelines for the remodeling potential of tibial shaft fractures according to the patient’s age.
Translation: Because of the subcutaneous nature of the tibial shaft, there may be concern about the effect of translocation on the clinical appearance. 100% translocation will result in a satisfactory outcome in the young child, whereas in the adolescent, the goal should be to achieve at least 50% apposition.
Strive for the bestFortunately for the treating surgeon, children have a tremendous capacity to remodel mal-alignment of their fractures, should it occur. This is no excuse for the treating surgeon not to make every attempt to obtain as anatomical an alignment as possible. If this cannot be achieved by conservative methods, then serious consideration should be given to achieving a satisfactory reduction by surgical means.
SummaryBy and large, the ability to remodel depends on the bone involved, the patient’s age, the proximity to the joint, and its orientation to the joint axis. In the typical long bone, 75% of the remodeling occurs by reorientation of the physis while appositional remodeling of the diaphysis can only be expected to contribute 25% to the remodeling process. The various values of acceptable alignment for each of the major fracture patterns listed should serve only as guidelines. The patient’s functional capacity and the surgeon’s experience should also be factors in determining whether to depend on the remodeling capacity of the specific fracture or to consider performing a more aggressive, invasive technique to achieve a satisfactory result.
References
Principles of fracture remodeling in children; Kaye E. Wilkins; Injury; Vol 36, 1, Supplement 1 , February 2005, Pages S3-S11
Do TT, Strub WM, et al. (2003) Reduction versus remodeling in paediatric distal forearm fractures: a preliminary cost analysis. J Pediatr. Orthop B; 12(2):109–115.
Price CT, Mencio GA (2001) Injuries to the shaft of the radius and ulna. Chapter 10 in Rockwood and Wilkins’ Fractures in Children. 5th ed. Philadelphia, PA: Lippincott, Williams and Wilkins. pp. 443–482.
Vorlat P, De Boeck H (2003) Bowing fractures of the forearm in children: a long-term follow up. Clin Orthop; 413: 233–237.
Kwon Y, Sarwark JF (2001) Proximal humerus, scapula and clavicle. Chapter 17 in: Rockwood and Wilkins’ Fractures in Children. 5th ed. Philadelphia, PA: Lippincott, Williams and Wilkins. pp. 741–806.
Beaty JH (1992) Fractures of the proximal humerus and shaft in children. AAOS Instr. Course Lect: 41:369–372.
Kasser JR, Beaty JH(2001) Femoral Shaft Fractures. Chapt. 22 in: Fractures in Children, Vol.III, 5th ed., Rockwood, Wilkins and Beaty eds. Lippincott Williams and Wilkins. Phila. PA. pp. 941–980.
Davids JR (1994) Rotational deformity and remodeling after fracture of the femur in children. Clin Orthp; 302:27–35.
Heinrich SD (2001) Fractures of the Shaft of the Tibia. Chapt.24 in: Fractures in Children, Vol.III, 5th ed., Rockwood, Wilkins and Beaty eds. Lippincott Williams and Wilkins. Phila. PA. p. 1077–1119.
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