Mf. Shepard et al., Effects of radial head excision and distal radial shortening on load-sharing in cadaver forearms, J BONE-AM V, 83A(1), 2001, pp. 92-100
Citations number
19
Categorie Soggetti
Ortopedics, Rehabilitation & Sport Medicine","da verificare
Background: The present study was performed to measure;changes in radioulna
r load-sharing in the cadaveric forearm following two orthopaedic surgical
procedures that often have varying results: radial head excision and distal
radial shortening. A better understanding of the biomechanical consequence
s of those procedures could aid surgeons in obtaining a more satisfactory c
linical outcome.
Methods: Miniature load-cells were inserted into the proximal part of the r
adius and the distal part of the ulna in twenty fresh-frozen cadaveric fore
arms. Load-cell forces, radial head displacement relative to the capitellum
, and local tension within the central band of the interosseous membrane we
re measured simultaneously as the wrist was loaded to 133.5 N in neutral pr
onation-supination and neutral radioulnar deviation. Testing was repeated a
fter incremental distal radial shortening and after removal of the radial h
ead.
Results: With the elbow flexed to 90 degrees and in valgus alignment (the r
adial head in contact with the capitellum), the mean force in the distal pa
rt of the ulna was 7.1% of the applied wrist force and the mean force in th
e in-terosseous membrane was 4.0%. With the elbow in varus alignment (a mea
n initial gap of 1.97 mm between the radial head and the capitellum), the r
espective mean values were 27.9% and 51.2%. After excision of the radial he
ad, the mean force in the distal part of the ulna increased to 42.4% of the
applied wrist force and the mean force in the interosseous membrane increa
sed to 58.8%, in both varus and valgus elbow alignment. The mean distal uln
ar force increased with progressive distal radial shortening in both varus
and valgus elbow alignment after 6 mm of radial shortening, the distal ulna
r force averaged 92.4% (in varus alignment) and 60.9% (in valgus alignment)
. Equal distal load-sharing between the radius and ulna occurred after appr
oximately 5 mm of radial shortening with the elbow in valgus alignment and
after approximately 2 mm of radial shortening with the elbow in varus align
ment. In valgus alignment, the force in the interosseous membrane was negli
gible after all degrees of radial shortening; in varus alignment, the mean
force in the interosseous membrane decreased from 51.2% (0 mm of distal rad
ial shortening) to 0% (6 mm of distal radial shortening) because of progres
sive slackening of the interosseous membrane.
Conclusions: Radial head excision shifted the applied wrist force that norm
ally would be transmitted to the elbow, through radial head-capitellar cont
act, to the interosseous membrane. The resulting proximal radial displaceme
nt created an ulnar-positive wrist and increased distal ulnar loading. Radi
al shortening and ulnar lengthening procedures have been designed to shift
the applied wrist force from the distal part of the radius to the distal pa
rt of the ulna; it is commonly assumed that these procedures have equivalen
t biomechanical effects. We found that radial shortening resulted in slacke
ning of the interosseous membrane, thereby negating its ability to transmit
load through the forearm. Slackening of the interosseous membrane would no
t be expected with distal ulnar lengthening procedures.
Clinical Relevance: When the radial head has been fractured or excised, the
mechanical status of the interosseous membrane is critical to the load-sha
ring process. If the interosseous membrane remains intact, distal ulnar loa
ds will be limited to less than half of the applied wrist force; if the int
erosseous membrane has been damaged, nearly the entire applied wrist force
will be shifted to the ulna. The amount of radial shortening or ulnar lengt
hening performed at the time of surgery during joint-leveling procedures ha
s been largely empirical. We found that distal ulnar load increased by appr
oximately 10% for each millimeter of radial shortening.