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The role of the interosseous membrane and triangular fibrocartilage complex in forearm stability
The Role of the Interosseous Membrane and Triangular Fibrocartilage Complex in Forearm Stability Richard S. Rabinowitz, MD, Terry R. light, MD, Robert M. Havey, BS, Prassad Gourineni, MD, Avinash G. Patwardhan, PhD, Mark J. Sartori, BS, Lori Vrbos, MS, Maywood, IL This study
investigated
fibrocartilage findings
suggest
capitellum
the primary
alone
both the midportion migration column.
occurs,
restraint radial
is disrupted,
of the IOM the radial
the IOM radial
migration
of the radius under of the IOM
acting
injuries.
to proximal
migration
migration
and TFCC.
can occur
little alteration
abuts the humerus,
as a restraint
portion
The intact
and triangular
radius
of the radius. under
axial
however,
and load
of the IOM
to proximal
radial
in load transfer.
load greater than 7 mm implies
(J Hand
(IOM)
compression.
further
is shifted
is the crucial migration.
We propose disruption
Our
abutting
After radial
in load or displacement
and TFCC are incompetent,
stump
and participates
an axial
membrane
of force from the hand to the humerus.
destabilizing
These data suggest that the central
sion within proximal
of forearm
up to 7 mm of proximal
TFCC or the IOM
roles of the interosseous
(TFCC) in the transmission
a spectrum
provides
excision,
the relative
complex
the head If the
is evident.
When
proximal
radial
back to the radial structural
subdivi-
The TFCC also resists that clinical
migration
of both the midportion
Surg 1994;19A:385-393.1
Compressive forces occurring from a fall on the outstretched hand often result in forearm bony and soft tissue injuries. Radial head fractures, as well as Galeazzi fracture is, frequently alter the relationship between the two forearm bones. Proximal migration of the radius often follows these injuries and may be associated with prominence of the subluxed or
From the Department of Orthopaedic Surgery, Loyola University Medical Center, Maywood, IL, and Orthopaedic Biomechanits Laboratory, Rehabilitation Research and Development Center, VA Hospital, Hines, IL. Received for publication March 16. 1993; accepted in revised form Oct. 2, 1993. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Richard S. Rabinowitz, MD, Loyola University Medical Center, Department of Orthopaedic Surgery, Building 54, Room 167, 2160 South First Avenue, Maywood, IL 60153.
dislocated distal ulna, hand weakness. limited range of motion, and chronic wrist painm4 The two forearm bones and the structures interconnecting them have unique roles in forearm stability and in force transmission from the hand to the humerus. The intact radius is the primary restraint to proximal radial migration, while the triangular fibrocartilage complex (TFCC) and interosseous membrane (IOM) have been identified as important secondary forearm stabilizers. Disruption of the bony integrity of the radius shifts restraint proximal migration to the soft tissue stabilizing structures. Prior studies have identified the importance of the TFCC and IOM, but the relative contribution of each in forearm stability and load transfer from the hand to the humerus remains uncertain.5-7 The purpose of this study was to identify the soft tissue elements stabilizing the radius and ulna to one another. We investigated the relative contributions of the IOM and TFCC in force transmission from The journal
of Hand
Surgery
385
386
Rabinowitz
et al. / IOM and TFCC
in Forearm Stability
the hand to the humerus and evaluated regions within the IOM. Materials
the various
and Methods
Six pairs of freshly frozen cadaveric upper limbs were procured. Three pairs were male and three were female. The age ranged from 30 to 72 years. The forearms were examined by x-ray films to eliminate bony pathology. The ulnar variance, evaluated using Epner’s technique, was neutral or negative in each limb.7 The experimental apparatus was constructed to allow unconstrained axial loading of the limbs in their physiologic position at the time of injury. To best simulate a fall on the outstretched hand, the specimens were tested in wrist extension, forearm pronation, and elbow extension. Load was applied via a pulley system that transmitted a 9.1 kg. vertical force to a Steinmann pin inserted transversely through the base of the index and middle finger metacarpals. Output forces were measured using two load cells, one to record the radial load and the second to record the ulnar load. A Watsmart optoelectronic motion measurement system (Watsmart, Northern Digital, Ontario, Canada) measured radial displacement and proximal migration. Two infrared-sensing cameras were mounted in a fixed spatial relationship to the specimen. Infrared-emitting diodes were attached to fixed points on the distal radius and ulna. The extent of displacement of each bone from its initial loaded position was registered three-dimensionally by the Watsmart cameras to an accuracy of t 0.5 mm. Preparation of the experimental limbs began with a transverse humeral osteotomy, 10 cm proximal to the elbow joint. An oscillating saw created a second osteotomy in the distal humerus perpendicular to the first, proceeding longitudinally towards the trochlear sulcus. Exposure of the TFCC and IOM was established through an extensile anterior approach. The incision extended from the intersection of Kaplan’s cardinal line and the radial border of the ring finger distally to the level of the transverse humeral osteotomy proximally. The flexor digitorum sublimi and profundi, along with the median nerve, were excised. Dissection of the pronator quadratus and flexor pollicus longus from attachments on the radius and IOM provided an unimpeded view of the TFCC and IOM. The remaining soft tissues and musculature were left intact. The proximal end of each specimen was then mounted into two custom-made humeral cups, maintaining the fixed spatial relationship between
the radial (lateral) and ulnar (medial) sides of the cut humerus. An osteotome completed the longitudinal humeral osteotomy into the trochlear groove, creating mechanically independent radial and ulnar columns. The experimental limbs were incorporated into the testing apparatus by attachment of the humeral cups to the two load cells (Fig. I). The experiment was divided into two phases. Phase 1 consisted of three testing groups, each with three limbs, and was designed to identify the relative importance of the three anatomic divisions within the IOM. Phase 2 consisted of a single test group with three limbs. In phase 1. the TFCC was sectioned prior to the IOM, while in phase 2 the TFCC was divided after the IOM. Altering the sequence of TFCC division in phases 1 and 2 helped define the contribution of the TFCC to forearm stability. In all 12 specimens, a constant 9.1 kg. force directed toward the humerus was applied at the hand. The forces generated across the radial and ulnar aspects of the elbow were recorded. Ulnar forces were transmitted to the medial humerus, while radial forces were transmitted to the lateral humerus. In phase 1, output forces and radial displacement were recorded simultaneously after each of the following sequential steps: (1) all restraints intact, (2) radial head excision, (3) TFCC division, (4) IOM division, and (5) proximal ligamentous complex division (oblique cord and annular ligament). In Step 4, the IOM was divided into thirds, based on the proximal and distal extent of the consistent central bank thickening, as described by Hotchkiss and Lafferty5 (Lafferty et al., unpublished data, 1990). Three different sequences of sectioning the distal, middle, and proximal IOM components were established. This created three groups of three specimens each. Specimens were randomly assigned to one of three groups: group IA: distal IOM, mid IOM, and proximal IOM; group IB: mid IOM, proximal IOM, distal IOM; and group 1C: proximal IOM, distal IOM, and mid IOM. In phase 2, the sequence was altered, so that the division of the TFCC occurred after complete sectioning of the IOM. Thus, in group 2A: the steps were (1) all restraints intact, (2) radial head excision, (3A) distal IOM division, (3B) mid IOM division, (3C) proximal IOM division, (4) TFCC division, and (5) proximal ligamentous complex division (oblique cord and annular ligament). Following the division of each structure, 30 seconds were allowed for creep and stress relaxation. The change in load and radial displacement associated with each sequential step was recorded simultaneously by an IBM 486 computer. At each of the seven steps, the computer sampled the load and dis-
The Journal of Hand Surgery / Vol. 19A No. 3 May 1994
387
Figure 1. Experimental limb mounted in the testing apparatus.
placement data at 100 Hz for 1 second; the computed average was used as the true measurement. The time interval from thawing of the specimens to completion of each experimental trial was less than 4 hours. The data were evaluated to determine overall variability and distribution. Power analysis techniques verified adequate sample size. One way multiple analysis of variance and Wilke’s lambda analysis were performed to compare the changes along with grouping intervals of radial load, radial displacement, ulnar load, and ulnar displacement. A significance level of .Ol was specified for added stringency.
Results Figure 2A-F depict normalized load transfer and displacement data for groups IA-C. The means and standard deviations are listed in Tables l-3. The displacement data demonstrate that, with all bone and soft tissue structures intact, the radius lies in the resting position and is nondisplaced. Up to 7 mm of proximal radial migration may occur underload after radial head excision. With the TFCC divided, little additional change was evident in any of the three testing scenarios until the mid-portion of the IOM was also sectioned. The load data correlated with the displacement data. Prior to sectioning any structures, 70% of the load was transmitted via the
388
Rabinowitz
et al. / IOM
and TFCC in Forearm
Stability
Q Ulna m Radius proximal Proximal Division Division Division Division
cstaListical1y Significant
@Radius AI1
B
D&I Mid Roximal Proximal Radial TFCC IOM IOM Complex Head Division IOM Division Division Division Division Ostectomy
Intact
*statistically Significant
iJ Ulna Q Radius All Intact
C
Radial FCC
Proximal Mid Pmximal D&l IOM Complex IOM Heed Division IOM Division Division Division Division Ostectomy
$Statisticaily Significant
Figure 2. Load distribution and radial migration data. Each bar represents the mean value for three specimens. Asterisk denotes a significant change from the previous step. (A) Phase 1A: load transfer data. Load shifts from the radius to the ulna after radial head excision. Load returns to the radius after the mid IOM cut. (B) Phase 1A: proximal radial migration data. Proximal radial migration after radial head excision with further migration after the mid IOM cut. (C) Phase 1B: load transfer data. Load shift from the radius to the ulna after radial head excision. Load returns to the radius after mid IOM cut. (Figure conrinues)
The journal of Hand Surgery I Vol. 19A No. 3 May 1994
389
n Radius
0
All Intact D
Radial WCC
Mid Proximal Distal Proximal IOM IOM Complex Head Division IOM Division Division Division Division Ostectomy
*Statistically Significant
100 90
80 70 60 50 40 30 20
IJ Ulna a Radius
10 0 All
E
Intact
Proximal Mid Proximal Distal Radial TFCC IOM IOM Complex Head Division IOM Division Division Division Division Ostectomy
*Statistically Significant
# Radius
F
All Intact
uadial
Head Ostectomy
TFCC Proximal Distal IOM Division IOM Division
Division
Mid IOM
Division
hximal Complex Division
*statistically Significant
2. (continued) (D) Phase 1B: proximal radial migration data. Some proximal radial migration after radial head excision with further proximal migration after the mid IOM cut. (E) Phase 1C: load transfer data. Load shift from the radius to the ulna after radial head excision. Load returns to the radius after the mid IOM cut. (F) Phase 1C: proximal radial migration data. Some proximal radial migration after radial head excision with further proximal migration after the mid IOM cut. (Figure continues)
Figure
390
Rabinowitz
et al. / IOM and TFCC in Forearm Stability 100 90 80 70 60 50 40 30 20 10 0
G
All Intact
All Intact
H
II
Q Ulna m Radius
Radial Distal Mid Proximal TFCC Proximal Head IOM IOM Division Complex IOM OstectQmyDivision Division Division Division
Radial DiStd Mid Fmximal WCC hximal Head IOM IOM Division Complex IOM Ostectomy Division Division Division Division
$Statistically Significant
*statistically Significant
Figure 2. (continued) (G) Phase 2A: load transfer data. Load shift from the radius to the ulna after radial head excision. Load returns to the radius after the TFCC cut. (H) Phase 2A: proximal radial migration data. Some proximal radial migration after radial head excision with further proximal migration after the TFCC cut.
radius to the capitellum, while 30% was transmitted via the ulna to the trochlea. Load was transferred from the radius to the ulna after radial head excision. With subsequent sectioning of both the TFCC and the midportion of the IOM, load was no longer shifted to the ulna and was primarily transmitted through the proximal radial stump to the capitellum. Figure 2G and H represent the normalized displacement and load transfer data in group 2A, when the TFCC was divided after the IOM. The means and standard deviations are listed in Table 4. Prior to sectioning or disrupting any structures, load data were similar to group 1 specimens. Proximal radial migration, with load transfer from the radius to the ulna, was again evident after radial head osteotomy in group 2A, as it was in groups IA-C. Additional significant radial migration and shift of load trans-
mission back through the radius occurred only after the entire IOM and TFCC had been sectioned. All four testing groups demonstrated up to 7 mm of proximal radial migration after radial head excision alone, when a 9.1 kg. axial force was applied. The change in both load and displacement data after radial head osteotomy was significant. In addition, significance was established for both the load and displacement data associated with the midportion of the IOM cut, when the TFCC was sectioned first, and for the TFCC cut, when the IOM was sectioned first.
Discussion Prior studies have differed in defining the contribution of the IOM and TFCC to forearm stability. Halls and Travill* studied force transmission
The Journal
of Hand
Surgery
I Vol.
___.
_____~.
Table 1. Phase IA: Load and Displacement --
Intact % Radial load % Ulnar load Radial displacement TFCC, triangular
(mm)
fibrocartilage
71 + 7 29 k 7 0.0 complex;
Radial Head Osteotomy
19A No. 3 May
391
1994
~~~ __
Data (Mean 2 SD) .~ _~~~ _. _~___~
TFCC Cut
Distal ZOM Cut
Mid ZOM Cut
Proximal ZOM Cut
Proximal Complex cut
3*5 97 -c 5 7*4
3+5 97 ‘- 5 724
62 k 21 38 f 21 12 k 1
71 5 22 29 + 22 13 k I
77 + 18 23 t 18 14 * 0
355 97 2 5 724
IOM, interosseous
membrane. -__
Table 2. Phase 1B: Load and Displacement
Intact % Radial load % Ulnar load Radial displacement Abbreviations
(mm)
86 _’ II 14 k 11 0.0
Radial Head Osteotomy __~
TFCC Cut ..~~ _~ 4+3 96 * 3 723
5*4 95 t 4 7t4
Data (Mean ? SD) Mid ZOM _~..cut
Proximal ZOM Cut
Distal IOM Cut
Proximal Complex cut
57 t I3 43 * 13 12 + 2
70 r 19 30 t 19 12 +- 2
88 r 7 12 2 7 12 k I
89 + 7 11 r 7 12 k I
same as in Table 1. ---__
-_
~~~~
~~.
Table 3. Phase iC: Load and Displacement Data (Mean t SD) -..- ~~~ .---~-.-.- ~_ ..__
Intact % Radial load % Ulnar load Radial displacement Abbreviations
(mm)
75 2 1 25 k 1 0.0
Radial Head Osteotomy 13 -t 6 87 r 6 3-1-3 ..~
TFCC Cut 10 +- 3 90 k 3 123 ~~ __ .___ ~
Proximal Distal LOOMCut ..-._IOM Cut 10 k 4 12 + 5 90 k 4 88 r 5 422 5k2
Mid ZOM cut
Proximai Comp fex cut
72 + 25 28 k 25 19 + 8
85 I 21 15 +- 21 22 + 9
same as in Table 1. -~~-_
Table 4. Phase 2A: Load and Displacement Data (Mean 2 SD) -. ___~~~~ ..~~~ -- ____ ~_____ Intact Radial load % Ulnar load Radial displacement
%
Abbreviations
(mm)
80 ‘- 8 20 * 8 0.0
Radial Head Osteotomy
Distal ZOM Mid ZOM Proximal IOM Cut cut ,. cut -~__._~______~~_
16 + 25 84 2 25 722
15 k 26 84 t 26 7*2
14 t 23 86 * 23 9 k 24
14 2 23 86 2 23 10 5 3
Proximal Complex TFCC Cut 82 2 10 18 k 10 14 + 2
Cut
86 + 9 14 + 9 14 k 2
same as in Table 1.
through the IOM and found no measurable influence of the IOM on percentage loads borne by the radius and ulna at the elbow joint. Moore et al.6 compared the roles of the TFCC and IOM in radial shortening after radial head excision and concluded that the TFCC is the major soft tissue restrain! preventing proximal radial migration, but shortening greater than 10 mm cannot occur without disruption of the IOM. They did not evaluate subdivisions within the IOM. Hotchkiss et al.5 reported that the central portion of the IOM contributes 71% to the mechanical stiffness of the forearm, while the TFCC contributes
only 8%. Lafferty et al. reported nearly equal contributions to forearm stability from the proximal one third of the IOM and TFCC (Lafferty et al., unpublished data, 1990). Reardon et al. found that the relative contribution to forearm stability by the TFCC and IOM varied with their order of sectioning (Reardon et al., unpublished data, 1991). The structures sectioned last appeared to carry most of the load. Reardon concurred with Lafferty’s conclusion, however, that within the IOM, the proximal one third is the most critical. Previous studies attempted to define the importance of anatomic divisions within the IOM but disa-
392
Rabinowitz
et al. / IOM and TFCC in Forearm
Stability
greed as to which component fibers were most important. These differences may reflect imprecise division boundaries, as well as variability of specimen morphology. Lafferty et al. demonstrated a consistent central thickening within the IOM in their dissections, which varied only in the number of central bands or cords. This was similar to our observations (Lafferty et al., unpublished data, 1990). To standardize the boundaries for division of the IOM into thirds in this study, we identified the thickened middle region in each forearm tested. The transition between the distal-middle IOM and middle-proximal IOM was labeled in each specimen with a stitch of 0 vicryl during dissection. In this fashion, the interface of the three IOM subdivision boundaries was clearly evident at the time of sectioning. Prior studies used only radial displacement data to identify the primary soft tissue stabilizers after mechanical disruption of the radius.7 Our study clearly isolated structures that when sacrified resulted in both radial displacement and load transfer. This enabled a definitive demonstration that within the IOM the mid-portion appears to be the crucial structural subdivision. This supports the previous observations of Lafferty et al. (unpublished data, 1990). Our study also identifies the TFCC as an important restraint to proximal radial migration and load transfer. This contrasts with the observations of Lafferty et al. (unpublished data, 1990), who noted only an 8% contribution of the TFCC to the longitudinal stiffness of the forearm. The increased role of the TFCC in our study reflects the analysis of combined displacement and load data obtained during the different sequences of sectioning the TFCC and the three subdivisions within the IOM. Our study examined an acute bone and soft tissue injury model in a laboratory setting. Specimens were tested in the physiologic position at the time of axial compressive injury (wrist extension, forearm pronation, and elbow extension) to accurately recreate upper extremity alignment during force transmission from the hand to the humerus. In this study, freshly frozen cadaveric limbs were used to further simulate the in vivo situation. Clinical studies of patients who have undergone radial head excision for treatment of comminuted radial head fractures document that some patients gradually develop wrist symptoms.‘-4,9 This suggests that after the original injury, the TFCC, mid IOM, or both may have been intact. Over time, dynamic physiologic loading may result in stretching of these soft tissue forearm stabilizers, permitting further proximal radial migration. One study was limited by sample size and did not address these possible chronic changes. Further studies are re-
quired to determine the role of soft tissue fatigue in late migration patterns. Because the interosseous membrane is not easily visualized, little is known about the pathologic anatomy of these forearm injuries. Whether failure of the IOM occurs in mid-substance or at the bone ligament interface remains uncertain. To date, magnetic resonance imaging has not consistently allowed evaluation of soft tissue injuries of the forearm. As technology improves, this imaging modality may prove beneficial in the early diagnosis of these injuries and help avoid the late complications that occur in the untreated situation. Loss of soft tissue linkage between the radius and ulna creates a “floating” radius, carpus, and hand complex. Surgical stabilization of this complex is difficult and may require creation of a one-bone forearm in the most severe injuries. This investigation suggests a spectrum of forearm destabilizing injuries. Normally, the intact radius articulating against the capitellum provides the primary restraint to proximal migration of the radius. After radial head excision, with all soft tissues intact, up to 7 mm of proximal radial migration can occur under axial load with the forearm in pronation. If either the TFCC or the IOM alone is disrupted, little additional change in displacement is seen. When both the mid IOM and the TFCC are incompetent, however, further proximal radial migration occurs, sufficient to allow abutment of the radial neck on the capitellum and shift load back to the radial column. Subluxation of the proximal radial stump may allow even further proximal radial migration. Our data suggest that the central portion of the IOM is the crucial region within the IOM in restraining proximal radial migration. The TFCC also acts to resist proximal radial migration. Clinical migration of the radius under axial loads greater than 6 or 7 mm implies disruption of both the mid IOM and TFCC.
References Edwards GS, Jupiter JB. Radial head fractures with acute distal radioulnar dislocation. Clin Orthop 1987; 234:61-9. Essex-Lopresti P. Fractures of the radial head with distal radioulnar dislocation. J Bone Joint Surg 1951; 33B:244-7. McDougall A, Glasgow JW. Subluxation of the inferior radio-ulnar joint complicating fracture of the radial head. J Bone Joint Surg 1957;39A:278-87. Taylor TK, O’Connor BT. The effect upon the inferior radio-ulnar joint of excision of the head of the radius in adults. J Bone Joint Surg 1964;46B:83-8.
The Journal
5. Hotchkiss RN, An KN, Sowa DT, Basta S, Weiland AJ. An anatomic and mechanical study of the interosseous membrane of the forearm: pathomechanics of proximal migration of the radius. J Hand Surg 1989; 14A:256-61. 6. Moore TM, Lester DK. Sarmiento A. The stabilizing effect of soft-tissue constraints in artifical Galeazzi fractures. Clin Orthop 1985;194:189-94. 7. Epner RA, Bowers WH, Guilford WB. Ulnar variance: the effect of wrist positioning and roentgen filming technique. J Hand Surg 1982;7:298-304. 8. Halls AA, Travill A. Transmission of pressures across the elbow joint. Anat Ret 1964;150:243-8. 9. Mason ML. Some observations on fractures of the
10. 11.
12.
13. 14.
of Hand
Surgery
I Vol.
19A No. 3 May
1994
393
head of the radius: with the review of one hundred cases. Br J Surg 1954;42:123-32. Fung YC. Biomechanics-mechanical properties of living tissues. New York: Springer-Verlag, 1981;22-6. Morrey BF, Chao EY, Hui FC. Biomechanical study of the elbow following excision of the radial head. J Bone Joint Surg 1979;61A:63-8. Morrey BF, An KN, Stortmont TJ. Force transmission through the radial head. J Bone Joint Surg 1988: 70A:250-6. Palmer AK, Werner FW. Biomechanics of the distal radioulnar joint. Clin Orthop 1984; 187:26-35. Werner JA. The function of antebrachial interosseous membrane. Anat Embryo1 1987;176:127-31.
investigated
fibrocartilage findings
suggest
capitellum
the primary
alone
both the midportion migration column.
occurs,
restraint radial
is disrupted,
of the IOM the radial
the IOM radial
migration
of the radius under of the IOM
acting
injuries.
to proximal
migration
migration
and TFCC.
can occur
little alteration
abuts the humerus,
as a restraint
portion
The intact
and triangular
radius
of the radius. under
axial
however,
and load
of the IOM
to proximal
radial
in load transfer.
load greater than 7 mm implies
(J Hand
(IOM)
compression.
further
is shifted
is the crucial migration.
We propose disruption
Our
abutting
After radial
in load or displacement
and TFCC are incompetent,
stump
and participates
an axial
membrane
of force from the hand to the humerus.
destabilizing
These data suggest that the central
sion within proximal
of forearm
up to 7 mm of proximal
TFCC or the IOM
roles of the interosseous
(TFCC) in the transmission
a spectrum
provides
excision,
the relative
complex
the head If the
is evident.
When
proximal
radial
back to the radial structural
subdivi-
The TFCC also resists that clinical
migration
of both the midportion
Surg 1994;19A:385-393.1
Compressive forces occurring from a fall on the outstretched hand often result in forearm bony and soft tissue injuries. Radial head fractures, as well as Galeazzi fracture is, frequently alter the relationship between the two forearm bones. Proximal migration of the radius often follows these injuries and may be associated with prominence of the subluxed or
From the Department of Orthopaedic Surgery, Loyola University Medical Center, Maywood, IL, and Orthopaedic Biomechanits Laboratory, Rehabilitation Research and Development Center, VA Hospital, Hines, IL. Received for publication March 16. 1993; accepted in revised form Oct. 2, 1993. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Richard S. Rabinowitz, MD, Loyola University Medical Center, Department of Orthopaedic Surgery, Building 54, Room 167, 2160 South First Avenue, Maywood, IL 60153.
dislocated distal ulna, hand weakness. limited range of motion, and chronic wrist painm4 The two forearm bones and the structures interconnecting them have unique roles in forearm stability and in force transmission from the hand to the humerus. The intact radius is the primary restraint to proximal radial migration, while the triangular fibrocartilage complex (TFCC) and interosseous membrane (IOM) have been identified as important secondary forearm stabilizers. Disruption of the bony integrity of the radius shifts restraint proximal migration to the soft tissue stabilizing structures. Prior studies have identified the importance of the TFCC and IOM, but the relative contribution of each in forearm stability and load transfer from the hand to the humerus remains uncertain.5-7 The purpose of this study was to identify the soft tissue elements stabilizing the radius and ulna to one another. We investigated the relative contributions of the IOM and TFCC in force transmission from The journal
of Hand
Surgery
385
386
Rabinowitz
et al. / IOM and TFCC
in Forearm Stability
the hand to the humerus and evaluated regions within the IOM. Materials
the various
and Methods
Six pairs of freshly frozen cadaveric upper limbs were procured. Three pairs were male and three were female. The age ranged from 30 to 72 years. The forearms were examined by x-ray films to eliminate bony pathology. The ulnar variance, evaluated using Epner’s technique, was neutral or negative in each limb.7 The experimental apparatus was constructed to allow unconstrained axial loading of the limbs in their physiologic position at the time of injury. To best simulate a fall on the outstretched hand, the specimens were tested in wrist extension, forearm pronation, and elbow extension. Load was applied via a pulley system that transmitted a 9.1 kg. vertical force to a Steinmann pin inserted transversely through the base of the index and middle finger metacarpals. Output forces were measured using two load cells, one to record the radial load and the second to record the ulnar load. A Watsmart optoelectronic motion measurement system (Watsmart, Northern Digital, Ontario, Canada) measured radial displacement and proximal migration. Two infrared-sensing cameras were mounted in a fixed spatial relationship to the specimen. Infrared-emitting diodes were attached to fixed points on the distal radius and ulna. The extent of displacement of each bone from its initial loaded position was registered three-dimensionally by the Watsmart cameras to an accuracy of t 0.5 mm. Preparation of the experimental limbs began with a transverse humeral osteotomy, 10 cm proximal to the elbow joint. An oscillating saw created a second osteotomy in the distal humerus perpendicular to the first, proceeding longitudinally towards the trochlear sulcus. Exposure of the TFCC and IOM was established through an extensile anterior approach. The incision extended from the intersection of Kaplan’s cardinal line and the radial border of the ring finger distally to the level of the transverse humeral osteotomy proximally. The flexor digitorum sublimi and profundi, along with the median nerve, were excised. Dissection of the pronator quadratus and flexor pollicus longus from attachments on the radius and IOM provided an unimpeded view of the TFCC and IOM. The remaining soft tissues and musculature were left intact. The proximal end of each specimen was then mounted into two custom-made humeral cups, maintaining the fixed spatial relationship between
the radial (lateral) and ulnar (medial) sides of the cut humerus. An osteotome completed the longitudinal humeral osteotomy into the trochlear groove, creating mechanically independent radial and ulnar columns. The experimental limbs were incorporated into the testing apparatus by attachment of the humeral cups to the two load cells (Fig. I). The experiment was divided into two phases. Phase 1 consisted of three testing groups, each with three limbs, and was designed to identify the relative importance of the three anatomic divisions within the IOM. Phase 2 consisted of a single test group with three limbs. In phase 1. the TFCC was sectioned prior to the IOM, while in phase 2 the TFCC was divided after the IOM. Altering the sequence of TFCC division in phases 1 and 2 helped define the contribution of the TFCC to forearm stability. In all 12 specimens, a constant 9.1 kg. force directed toward the humerus was applied at the hand. The forces generated across the radial and ulnar aspects of the elbow were recorded. Ulnar forces were transmitted to the medial humerus, while radial forces were transmitted to the lateral humerus. In phase 1, output forces and radial displacement were recorded simultaneously after each of the following sequential steps: (1) all restraints intact, (2) radial head excision, (3) TFCC division, (4) IOM division, and (5) proximal ligamentous complex division (oblique cord and annular ligament). In Step 4, the IOM was divided into thirds, based on the proximal and distal extent of the consistent central bank thickening, as described by Hotchkiss and Lafferty5 (Lafferty et al., unpublished data, 1990). Three different sequences of sectioning the distal, middle, and proximal IOM components were established. This created three groups of three specimens each. Specimens were randomly assigned to one of three groups: group IA: distal IOM, mid IOM, and proximal IOM; group IB: mid IOM, proximal IOM, distal IOM; and group 1C: proximal IOM, distal IOM, and mid IOM. In phase 2, the sequence was altered, so that the division of the TFCC occurred after complete sectioning of the IOM. Thus, in group 2A: the steps were (1) all restraints intact, (2) radial head excision, (3A) distal IOM division, (3B) mid IOM division, (3C) proximal IOM division, (4) TFCC division, and (5) proximal ligamentous complex division (oblique cord and annular ligament). Following the division of each structure, 30 seconds were allowed for creep and stress relaxation. The change in load and radial displacement associated with each sequential step was recorded simultaneously by an IBM 486 computer. At each of the seven steps, the computer sampled the load and dis-
The Journal of Hand Surgery / Vol. 19A No. 3 May 1994
387
Figure 1. Experimental limb mounted in the testing apparatus.
placement data at 100 Hz for 1 second; the computed average was used as the true measurement. The time interval from thawing of the specimens to completion of each experimental trial was less than 4 hours. The data were evaluated to determine overall variability and distribution. Power analysis techniques verified adequate sample size. One way multiple analysis of variance and Wilke’s lambda analysis were performed to compare the changes along with grouping intervals of radial load, radial displacement, ulnar load, and ulnar displacement. A significance level of .Ol was specified for added stringency.
Results Figure 2A-F depict normalized load transfer and displacement data for groups IA-C. The means and standard deviations are listed in Tables l-3. The displacement data demonstrate that, with all bone and soft tissue structures intact, the radius lies in the resting position and is nondisplaced. Up to 7 mm of proximal radial migration may occur underload after radial head excision. With the TFCC divided, little additional change was evident in any of the three testing scenarios until the mid-portion of the IOM was also sectioned. The load data correlated with the displacement data. Prior to sectioning any structures, 70% of the load was transmitted via the
388
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et al. / IOM
and TFCC in Forearm
Stability
Q Ulna m Radius proximal Proximal Division Division Division Division
cstaListical1y Significant
@Radius AI1
B
D&I Mid Roximal Proximal Radial TFCC IOM IOM Complex Head Division IOM Division Division Division Division Ostectomy
Intact
*statistically Significant
iJ Ulna Q Radius All Intact
C
Radial FCC
Proximal Mid Pmximal D&l IOM Complex IOM Heed Division IOM Division Division Division Division Ostectomy
$Statisticaily Significant
Figure 2. Load distribution and radial migration data. Each bar represents the mean value for three specimens. Asterisk denotes a significant change from the previous step. (A) Phase 1A: load transfer data. Load shifts from the radius to the ulna after radial head excision. Load returns to the radius after the mid IOM cut. (B) Phase 1A: proximal radial migration data. Proximal radial migration after radial head excision with further migration after the mid IOM cut. (C) Phase 1B: load transfer data. Load shift from the radius to the ulna after radial head excision. Load returns to the radius after mid IOM cut. (Figure conrinues)
The journal of Hand Surgery I Vol. 19A No. 3 May 1994
389
n Radius
0
All Intact D
Radial WCC
Mid Proximal Distal Proximal IOM IOM Complex Head Division IOM Division Division Division Division Ostectomy
*Statistically Significant
100 90
80 70 60 50 40 30 20
IJ Ulna a Radius
10 0 All
E
Intact
Proximal Mid Proximal Distal Radial TFCC IOM IOM Complex Head Division IOM Division Division Division Division Ostectomy
*Statistically Significant
# Radius
F
All Intact
uadial
Head Ostectomy
TFCC Proximal Distal IOM Division IOM Division
Division
Mid IOM
Division
hximal Complex Division
*statistically Significant
2. (continued) (D) Phase 1B: proximal radial migration data. Some proximal radial migration after radial head excision with further proximal migration after the mid IOM cut. (E) Phase 1C: load transfer data. Load shift from the radius to the ulna after radial head excision. Load returns to the radius after the mid IOM cut. (F) Phase 1C: proximal radial migration data. Some proximal radial migration after radial head excision with further proximal migration after the mid IOM cut. (Figure continues)
Figure
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G
All Intact
All Intact
H
II
Q Ulna m Radius
Radial Distal Mid Proximal TFCC Proximal Head IOM IOM Division Complex IOM OstectQmyDivision Division Division Division
Radial DiStd Mid Fmximal WCC hximal Head IOM IOM Division Complex IOM Ostectomy Division Division Division Division
$Statistically Significant
*statistically Significant
Figure 2. (continued) (G) Phase 2A: load transfer data. Load shift from the radius to the ulna after radial head excision. Load returns to the radius after the TFCC cut. (H) Phase 2A: proximal radial migration data. Some proximal radial migration after radial head excision with further proximal migration after the TFCC cut.
radius to the capitellum, while 30% was transmitted via the ulna to the trochlea. Load was transferred from the radius to the ulna after radial head excision. With subsequent sectioning of both the TFCC and the midportion of the IOM, load was no longer shifted to the ulna and was primarily transmitted through the proximal radial stump to the capitellum. Figure 2G and H represent the normalized displacement and load transfer data in group 2A, when the TFCC was divided after the IOM. The means and standard deviations are listed in Table 4. Prior to sectioning or disrupting any structures, load data were similar to group 1 specimens. Proximal radial migration, with load transfer from the radius to the ulna, was again evident after radial head osteotomy in group 2A, as it was in groups IA-C. Additional significant radial migration and shift of load trans-
mission back through the radius occurred only after the entire IOM and TFCC had been sectioned. All four testing groups demonstrated up to 7 mm of proximal radial migration after radial head excision alone, when a 9.1 kg. axial force was applied. The change in both load and displacement data after radial head osteotomy was significant. In addition, significance was established for both the load and displacement data associated with the midportion of the IOM cut, when the TFCC was sectioned first, and for the TFCC cut, when the IOM was sectioned first.
Discussion Prior studies have differed in defining the contribution of the IOM and TFCC to forearm stability. Halls and Travill* studied force transmission
The Journal
of Hand
Surgery
I Vol.
___.
_____~.
Table 1. Phase IA: Load and Displacement --
Intact % Radial load % Ulnar load Radial displacement TFCC, triangular
(mm)
fibrocartilage
71 + 7 29 k 7 0.0 complex;
Radial Head Osteotomy
19A No. 3 May
391
1994
~~~ __
Data (Mean 2 SD) .~ _~~~ _. _~___~
TFCC Cut
Distal ZOM Cut
Mid ZOM Cut
Proximal ZOM Cut
Proximal Complex cut
3*5 97 -c 5 7*4
3+5 97 ‘- 5 724
62 k 21 38 f 21 12 k 1
71 5 22 29 + 22 13 k I
77 + 18 23 t 18 14 * 0
355 97 2 5 724
IOM, interosseous
membrane. -__
Table 2. Phase 1B: Load and Displacement
Intact % Radial load % Ulnar load Radial displacement Abbreviations
(mm)
86 _’ II 14 k 11 0.0
Radial Head Osteotomy __~
TFCC Cut ..~~ _~ 4+3 96 * 3 723
5*4 95 t 4 7t4
Data (Mean ? SD) Mid ZOM _~..cut
Proximal ZOM Cut
Distal IOM Cut
Proximal Complex cut
57 t I3 43 * 13 12 + 2
70 r 19 30 t 19 12 +- 2
88 r 7 12 2 7 12 k I
89 + 7 11 r 7 12 k I
same as in Table 1. ---__
-_
~~~~
~~.
Table 3. Phase iC: Load and Displacement Data (Mean t SD) -..- ~~~ .---~-.-.- ~_ ..__
Intact % Radial load % Ulnar load Radial displacement Abbreviations
(mm)
75 2 1 25 k 1 0.0
Radial Head Osteotomy 13 -t 6 87 r 6 3-1-3 ..~
TFCC Cut 10 +- 3 90 k 3 123 ~~ __ .___ ~
Proximal Distal LOOMCut ..-._IOM Cut 10 k 4 12 + 5 90 k 4 88 r 5 422 5k2
Mid ZOM cut
Proximai Comp fex cut
72 + 25 28 k 25 19 + 8
85 I 21 15 +- 21 22 + 9
same as in Table 1. -~~-_
Table 4. Phase 2A: Load and Displacement Data (Mean 2 SD) -. ___~~~~ ..~~~ -- ____ ~_____ Intact Radial load % Ulnar load Radial displacement
%
Abbreviations
(mm)
80 ‘- 8 20 * 8 0.0
Radial Head Osteotomy
Distal ZOM Mid ZOM Proximal IOM Cut cut ,. cut -~__._~______~~_
16 + 25 84 2 25 722
15 k 26 84 t 26 7*2
14 t 23 86 * 23 9 k 24
14 2 23 86 2 23 10 5 3
Proximal Complex TFCC Cut 82 2 10 18 k 10 14 + 2
Cut
86 + 9 14 + 9 14 k 2
same as in Table 1.
through the IOM and found no measurable influence of the IOM on percentage loads borne by the radius and ulna at the elbow joint. Moore et al.6 compared the roles of the TFCC and IOM in radial shortening after radial head excision and concluded that the TFCC is the major soft tissue restrain! preventing proximal radial migration, but shortening greater than 10 mm cannot occur without disruption of the IOM. They did not evaluate subdivisions within the IOM. Hotchkiss et al.5 reported that the central portion of the IOM contributes 71% to the mechanical stiffness of the forearm, while the TFCC contributes
only 8%. Lafferty et al. reported nearly equal contributions to forearm stability from the proximal one third of the IOM and TFCC (Lafferty et al., unpublished data, 1990). Reardon et al. found that the relative contribution to forearm stability by the TFCC and IOM varied with their order of sectioning (Reardon et al., unpublished data, 1991). The structures sectioned last appeared to carry most of the load. Reardon concurred with Lafferty’s conclusion, however, that within the IOM, the proximal one third is the most critical. Previous studies attempted to define the importance of anatomic divisions within the IOM but disa-
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Stability
greed as to which component fibers were most important. These differences may reflect imprecise division boundaries, as well as variability of specimen morphology. Lafferty et al. demonstrated a consistent central thickening within the IOM in their dissections, which varied only in the number of central bands or cords. This was similar to our observations (Lafferty et al., unpublished data, 1990). To standardize the boundaries for division of the IOM into thirds in this study, we identified the thickened middle region in each forearm tested. The transition between the distal-middle IOM and middle-proximal IOM was labeled in each specimen with a stitch of 0 vicryl during dissection. In this fashion, the interface of the three IOM subdivision boundaries was clearly evident at the time of sectioning. Prior studies used only radial displacement data to identify the primary soft tissue stabilizers after mechanical disruption of the radius.7 Our study clearly isolated structures that when sacrified resulted in both radial displacement and load transfer. This enabled a definitive demonstration that within the IOM the mid-portion appears to be the crucial structural subdivision. This supports the previous observations of Lafferty et al. (unpublished data, 1990). Our study also identifies the TFCC as an important restraint to proximal radial migration and load transfer. This contrasts with the observations of Lafferty et al. (unpublished data, 1990), who noted only an 8% contribution of the TFCC to the longitudinal stiffness of the forearm. The increased role of the TFCC in our study reflects the analysis of combined displacement and load data obtained during the different sequences of sectioning the TFCC and the three subdivisions within the IOM. Our study examined an acute bone and soft tissue injury model in a laboratory setting. Specimens were tested in the physiologic position at the time of axial compressive injury (wrist extension, forearm pronation, and elbow extension) to accurately recreate upper extremity alignment during force transmission from the hand to the humerus. In this study, freshly frozen cadaveric limbs were used to further simulate the in vivo situation. Clinical studies of patients who have undergone radial head excision for treatment of comminuted radial head fractures document that some patients gradually develop wrist symptoms.‘-4,9 This suggests that after the original injury, the TFCC, mid IOM, or both may have been intact. Over time, dynamic physiologic loading may result in stretching of these soft tissue forearm stabilizers, permitting further proximal radial migration. One study was limited by sample size and did not address these possible chronic changes. Further studies are re-
quired to determine the role of soft tissue fatigue in late migration patterns. Because the interosseous membrane is not easily visualized, little is known about the pathologic anatomy of these forearm injuries. Whether failure of the IOM occurs in mid-substance or at the bone ligament interface remains uncertain. To date, magnetic resonance imaging has not consistently allowed evaluation of soft tissue injuries of the forearm. As technology improves, this imaging modality may prove beneficial in the early diagnosis of these injuries and help avoid the late complications that occur in the untreated situation. Loss of soft tissue linkage between the radius and ulna creates a “floating” radius, carpus, and hand complex. Surgical stabilization of this complex is difficult and may require creation of a one-bone forearm in the most severe injuries. This investigation suggests a spectrum of forearm destabilizing injuries. Normally, the intact radius articulating against the capitellum provides the primary restraint to proximal migration of the radius. After radial head excision, with all soft tissues intact, up to 7 mm of proximal radial migration can occur under axial load with the forearm in pronation. If either the TFCC or the IOM alone is disrupted, little additional change in displacement is seen. When both the mid IOM and the TFCC are incompetent, however, further proximal radial migration occurs, sufficient to allow abutment of the radial neck on the capitellum and shift load back to the radial column. Subluxation of the proximal radial stump may allow even further proximal radial migration. Our data suggest that the central portion of the IOM is the crucial region within the IOM in restraining proximal radial migration. The TFCC also acts to resist proximal radial migration. Clinical migration of the radius under axial loads greater than 6 or 7 mm implies disruption of both the mid IOM and TFCC.
References Edwards GS, Jupiter JB. Radial head fractures with acute distal radioulnar dislocation. Clin Orthop 1987; 234:61-9. Essex-Lopresti P. Fractures of the radial head with distal radioulnar dislocation. J Bone Joint Surg 1951; 33B:244-7. McDougall A, Glasgow JW. Subluxation of the inferior radio-ulnar joint complicating fracture of the radial head. J Bone Joint Surg 1957;39A:278-87. Taylor TK, O’Connor BT. The effect upon the inferior radio-ulnar joint of excision of the head of the radius in adults. J Bone Joint Surg 1964;46B:83-8.
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5. Hotchkiss RN, An KN, Sowa DT, Basta S, Weiland AJ. An anatomic and mechanical study of the interosseous membrane of the forearm: pathomechanics of proximal migration of the radius. J Hand Surg 1989; 14A:256-61. 6. Moore TM, Lester DK. Sarmiento A. The stabilizing effect of soft-tissue constraints in artifical Galeazzi fractures. Clin Orthop 1985;194:189-94. 7. Epner RA, Bowers WH, Guilford WB. Ulnar variance: the effect of wrist positioning and roentgen filming technique. J Hand Surg 1982;7:298-304. 8. Halls AA, Travill A. Transmission of pressures across the elbow joint. Anat Ret 1964;150:243-8. 9. Mason ML. Some observations on fractures of the
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head of the radius: with the review of one hundred cases. Br J Surg 1954;42:123-32. Fung YC. Biomechanics-mechanical properties of living tissues. New York: Springer-Verlag, 1981;22-6. Morrey BF, Chao EY, Hui FC. Biomechanical study of the elbow following excision of the radial head. J Bone Joint Surg 1979;61A:63-8. Morrey BF, An KN, Stortmont TJ. Force transmission through the radial head. J Bone Joint Surg 1988: 70A:250-6. Palmer AK, Werner FW. Biomechanics of the distal radioulnar joint. Clin Orthop 1984; 187:26-35. Werner JA. The function of antebrachial interosseous membrane. Anat Embryo1 1987;176:127-31.