- Email: [email protected]
Reconstruction of the interosseous membrane of the forearm in cadavers
Reconstruction of the Interosseous Membrane of the Forearm in Cadavers James R. Skahen III, MD, Andrew K. Palmer, MD, Frederick W. Werner, MME, Maria D. Fortino, BS, Syracuse, NY The biomechanical function of the interosseous membrane of the forearm was examined in 12 fresh cadaver forearms. The strain in the central band of the interosseous membrane was found to be greatest in full pronation and was significantly increased with excision of the radial head. The proximal/distal location of the lunate fossa of the radius with respect to the ulna was measured and was found to be most distal in supination and most proximal in pronation, in both the intact specimen and after excision of the radial head. Serial sectioning of the interosseous membrane and the triangular fibrocartilage complex (TFCC) demonstrated that both the central band and the TFCC are important to the axial stability of the forearm. Reconstruction of the central band, using a graft based upon the flexor carpi radialis, was performed in all 12 specimens after the interosseous membrane and the TFCC were sectioned. It was successful in preventing complete migration of the radius to the capitellum, but it was not capable of completely restoring the longitudinal stability of the forearm. Central band reconstruction as described here has not been performed in the clinical setting and is not advocated for clinical application at this time. (J Hand Surg 1997;22A:986-994.)
Fracture of the radial head with dislocation of the distal radioulnar joint (DRUJ) was first described by Curr and Coe in 1946. 2 It was not until 1951 that this injury received more widespread recognition, and it has since been known as the Essex-Lopresti lesion. 2 EssexLopresti believed that this injury must also include disruption of the interosseous membrane (IOM) of the forearm. In the last 2 decades, authors have suggested that this injury might also include disruption of the triangular fibrocartilage complex (TFCC). 3~
From the Department of Orthopedic Surgery, State University of NewYorkHealthScienceCenter, Syracuse,NY. Funded in part by a grant from the AmericanSocietyfor Surgeryof the Hand. Received forpublicationMarch 19, 1996; acceptedin revised form April 16, 1997. No benefitsin any formhave been receivedor will be receivedfroma commercialpartyrelateddirectlyor indirectlyto the subjectof this article. Reprint requests: FrederickW. Werner,MME, Departmentof Orthopedic Surgery, SUNY Health Science Center, 750 E. Adams Street, Syracuse,NY 13210.
986
The Journal of Hand Surgery
Proximal migration of the radius after resection of the radial head in the treatment o f the EssexLopresti lesion can result in pain and disability o f the DRUJ. It is also possible that proximal migration of the radius after radial head excision can occur over time as the IOM attenuates and fails secondary to chronic force overload. Resection of the radial head alone can exacerbate this problem and should be avoided if at all possible. Current surgical approaches to this problem include resection o f the radial head and pinning o f the DRUJ until the soft tissues have healed, silicone arthroplasty of the proximal radius, and creation of a single-bone forearm. Results o f these procedures are inconsistent and fail to address the entire problem. Sellman et al. investigated reconstructive strategies for radioulnar dissociation from a biomechanical perspective using silicone and titanium implants with and without a braided polyester cord substitute for the central band (CB) of the IOM: they obtained variable results. 6
The Journal of Hand Surgery / Vol. 22A No. 6 November 1997
In an earlier article, we described the anatomy of the IOM of the forearm in detail. 7 We demonstrated that when the radial head is lost, the CB of the IOM resists proximal migration of the radius, by transferring load to the ulna. Theoretically in an EssexLopresti lesion, reconstruction of a damaged IOM of the forearm with a load-sharing graft might prevent proximal migration of the radius. Such a procedure might serve to improve the long-term outcome of this difficult injury. The first goal of this study was to clarify the axial stabilizing roles of the forearm, specifically the TFCC and the IOM. The second goal was to develop a surgical protocol that would restore axial stability after an Essex-Lopresti injury by providing a graft capable of transferring load from the radius to the ulna, thus preventing proximal migration of the radius.
Materials and Methods Biomechanics
Twelve fresh-frozen upper extremities were studied. Each specimen was transected at the junction of the middle and distal thirds of the humerus. All specimens were dissected free of investing soft tissues, leaving the structures of the hand, wrist, IOM, and elbow intact. The extensor carpi radialis brevis, extensor carpi radialis longus, extensor carpi ulnaris, flexor carpi ulnaris, and flexor carpi radialis (FCR) tendons were preserved for physiologic loading of the wrist and forearm. The tendons of the pronator teres and biceps were also preserved to allow dynamic pronation and supination by alternate manual loading of these tendons. A customized mounting frame was designed to hold each specimen in a standard position. The forearm was maintained in a vertical position. The ulnohumeral joint was pinned at 90~ the radiohumeral joint was left free to pronate and supinate. The wrist was maintained in 0 ~ of extension by means of a 1.58-mm (0.062-inch) Steinmann pin placed in the medullary canal of the middle finger metacarpal. This pin also permitted unconstrained forearm rotation around the fixed ulna. A large intermedullary pin was cemented into the humeral stump of each specimen, serving to anchor each specimen to the testing frame. Loading of the forearm and wrist was done by applying 22.2 N (5 lb.) of load to each of the primary wrist motors, for a total of 89 N applied across the wrist. 8 A differential voltage reluctance transducer ([DVRT] MicroStrain, Inc, Burlington, VT) was embedded in
987
the midsubstance of the CB on each specimen, as in our previous study. 7 This small displacement transducer allowed us to calculate the strain in the CB during physiologic loading. The displacement data, later converted to strain, were recorded at a rate of 10 Hz. A 3 Space electromagnetic tracking system ~0 was also used in this study. Sensors were mounted on the dorsal surface of the distal ulna and radius. Their three-dimensional angular and translation locations with respect to the reference source were recorded throughout the experiment by computer acquisition of data. These measurements were synchronized with the strain measurement data and recorded simultaneously. This system allowed an accurate and reproducible three-dimensional record of the position of the radius and ulna throughout the experiment. At the conclusion of the experiment, the articulating surfaces and coronal outlines of the distal radius and ulna were digitized using this same system and recorded relative to the electromagnetic source. Mathematic transformation of the data then permitted us to determine the three-dimensional location of the distal articulating surfaces of the radius, at any supination and pronation position, relative to the ulna. Strain in the CB was recorded during dynamic pronation and supination. Each of the 12 specimens was tested in the intact state and then again after the radial head was excised. Zero strain was defined in a stationary neutral forearm rotation in the intact specimen with the physiologic load applied. To analyze the relative contribution of the IOM of the forearm and the TFCC to the axial stability of the forearm, we divided the specimens into 2 groups of 6 each. The motions of the radius and ulna along with the strain in the CB were recorded during dynamic forearm rotation as the IOM and the TFCC were serially divided. The motion data of the radius and ulna were used to compute the relative position of the lunate fossa of the radius with respect to the head of the ulna. In group A, the order of sectioning was proximal to distal. Measurements were first made with the forearm intact, then after radial head excision, after sectioning of the IOM proximal to but not including the CB, after sectioning of the CB, after sectioning of the distal IOM, and finally after sectioning of the TFCC. In group B, the order of sectioning was distal to proximal. Measurements were first made with the forearm intact, after radial head excision, after sectioning of the TFCC, after sectioning of the distal IOM up to but not including
988
Skahen et al. / Interosseous Membrane: Central Band Repair
the CB, after sectioning of the CB, and finally after sectioning of the proximal IOM.
Central Band Reconstruction Our anatomic study v of the IOM of the forearm demonstrated that the CB was the most dominant and consistent structure. The biomechanical data indicated that the CB experienced strain in a dynamic fashion, dependent on forearm rotation. 8 In addition, radial head excision dramatically increased the strain experienced by the CB. On the basis of this information, we developed a surgical protocol for the reconstruction of the CB. Our goal was to restore axial stability to the forearm after an Essex-Lopresti injury by providing a graft capable of transferring load from the radius to the ulna, thus preventing proximal migration of the radius. A reconstructive procedure was performed in each of the 12 fresh forearms after serial sectioning of the TFCC and IOC. It was believed that after these sectionings, each specimen had in essence an EssexLopresti injury. First, the DRUJ of each specimen was pinned in neutral forearm rotation, in the position of ulnar variance native to each specimen. The original native ulnar variance of each specimen had been recorded before starting the experiment. A neutral forearm rotation position was chosen, since in the intact specimen this position produces strain in the CB that is generally midway between maximum and minimum strain. In addition, we found that maximum tensioning of the graft in full pronation severely limited supination, and tended to force the radius distally. The FCR was harvested from each specimen during initial preparation. Our preliminary studies found that the palmaris longus and only one half of the FCR were inadequate as graft material. They were unable to support the radius under physiologic loading. For this reason, the full FCR tendon was used for grafting purposes. The origin and insertion of the CB of each specimen was identified in the intact specimen with a surgical marker prior to the start of the biomechanical study. Graft length was then directly measured in the direction of the fibers of the CB and the FCR was cut to length. Our goal was to place the graft in the position and orientation of the native CB for each specimen. To anchor the graft within the substance of the radius and ulna, a 6.35-mm (1/4-inch) diameter drill hole was placed in the radius and ulna at the points of origin and insertion. These holes were placed in the coronal plane and directed to the orientation of the native CB fibers.
The ends of the FCR autograft were then secured with #5 nonabsorbable braided polyester suture, with a standard whipstitch used to prevent pullout. A suture passer was then used to pass the graft, through the previously drilled holes, from the radius to the ulna. The radial limb of the graft was then secured to the radial cortex of the radius by tying the suture over a nylon button. The graft was then maximally tensioned by pulling the sutures in the ulnar limb of the graft. The ulnar limb of the graft was then tied over a nylon button. Figure 1 illustrates the grafting procedure. During the entire reconstructive procedure, native ulnar variance was maintained by a pin in the DRUJ. In addition, each specimen was reconstructed with the forearm in the unloaded state. No attempt to repair the TFCC was made in this study.
Results Strain in the Central Band of the Interosseous Membrane Figure 2 illustrates the strain experienced by the CB under physiologic loading as the forearm is dynamically rotated from pronation to supination. Since this graph represents the average data from 11 specimens, it only spans the range in supination and pronation common to all 11. A single specimen was deleted from this analysis because of accidental displacement of the DVRT barbs during experimentation, and data salvage was not possible. In the intact specimens, strain in the CB was the least in full supination and it progressively increased to a maximum in full pronation. This relationship was not dependent on direction of rotation, as data taken during full supination to full pronation demonstrated the same trend. Excision of the radial head did not change this relationship; rather, the strain in the CB was universally greater throughout forearm rotation. This increase in strain after radial head excision was statistically significant from full pronation to 36 ~ of supination (one-tailed paired t-test, p < .05). Table 1 represents strains in the CB for specimens in group A (soft tissue release from proximal to distal) at the neutral forearm rotation position. Simple excision of the radial head resulted in a 0.67% increase in strain. Release of the proximal IOM from the elbow up to but not including the CB caused an increase of 1.64%. In a pilot study, we have shown that a force of 50 N applied directly to the CB can cause a 1% increase in strain in the CB, suggesting that these strain levels are not trivial. Similar data for group B (soft tissue release from distal to proximal) are presented in Table 2. Removal
The Journal of Hand Surgery/ Vol. 22A No. 6 November 1997 989
Figure 1. A reconstructive graft for the central band of the interosseous membrane. Flexor carpi radialis (FCR) autograft is secured in the position and orientation of the original central band. Each end of the FCR is held with #5 nonabsorbable braided polyester suture using a whipstitch, passed through oblique holes in the radius and ulna, maximally tensioned, and tied to a nylon button. The ulna is on the left, the radius is on the right, and distal is at the top.
of the radial head in the loaded specimen resulted in an increase in strain comparable to that in group A. Whereas excision of the T F C C did not alter the strain in the CB, release of the I O M from the wrist up to but not including the CB resulted in an increased strain of 1.37%.
Proximal Migration of the Radius The location of the lunate fossa of the radius with respect to the position of the ulnar head was computed from the data recorded throughout the experiment with the 3 Space tracking system. In the intact
1-
o., f _ _ : _ 0.8
% STRAIN 0.4 IN CB 0"2 0
"0"2t -0.4
.5o
-,io
SUPINATION
-1'o
o
1'o
FOREARMROTATION (deg)
2'0
3'0
4'o
PRONATION
Figure 2. Average changes in the strain in the central band (CB) under physiologic loading as the forearm was dynamically rotated from pronation to supination. Strain was greatest in pronation and increased with excision of the radial head. The increase in strain with radial head excision was statistically significant from full pronation to 36 ~ of supination.
990
Skahen et al. / Interosseous Membrane: Central Band Repair
Table 1. Percent Strain in the Interosseous Membrane Central Band at 0~ of Forearm Rotation for First Set of Fresh Limbs (n = 4), With Serial Soft Tissue Release From Proximal to Distal* % Strain (SD)
Intact forearm Radial head removed Excision of the proximal interosseous membrane from the elbowjoint up to but not includingthe central band
-0.06 (0.19) 0.67 (0.42) 1.64 (0.99)
* Data availablefrom only 4 specimens, since strain data were not initially recorded with partial excision of the interosseous membranein all specimens.
specimen, the position of the lunate fossa of the radius is most distal in full supination and most proximal in full pronation. This relationship is maintained even after the radial head has been removed. Figure 3 represents the average proximal migration of the lunate fossa of the radius for the 12 specimens. The relative location of the lunate fossa of the radius to the ulnar head is given in Table 3 and Figure 4 for the group A specimens. The average of all 6 specimens is given in Table 3 for 3 static positions: neutral forearm rotation, full pronation, and full supination. Figure 4 shows a coronal view of the distal radius and ulna for 1 specimen at neutral forearm rotation. In supination, statistically significant (oneway repeated-measures analysis of variance, 95% confidence interval [CI]) proximal migration of the radius occurred after the radial head was excised and the proximal and CB regions of the IOM were sectioned. In neutral and pronation, significant migration occurred only after the distal portion of the IOM had been sectioned as well. Complete proximal migration of the radius to the point where the stump abutted the capitellum occurred only after complete release of the IOM and the TFCC. The apparent increased proximal migration of the radius in the
Table 2. Percent Strain in the Interosseous Membrane Central Band at 0 ~ of Forearm Rotation for Second Set of Fresh Limbs (n = 6), With Serial Soft Tissue Release From Distal to Proximal % Strain (SD)
Intact forearm Radial head removed Triangular fibrocartilagecomplex excised Excision of the distal interosseousmembrane from the wrist up to but not includingthe central band
0.08 (0.22) 0.59 (0.69) 0.54 (0.83) 1.37 (0.50)
pronated positions is due to anterior and medial displacement of the proximal radius, in turn caused by the action of the pronator teres in a grossly unstable forearm. In other words, the proximal radius was no longer in contact with the capitellum and was therefore free to migrate to a more proximal position. The relative position of the lunate fossa of the radius with respect to the ulnar head for group B specimens is presented in Table 4 and Figure 5. Table 4 represents the average data for the 6 specimens, in the 3 specified static positions. Statistically significant proximal migration of the radius did not occur until the radial head was excised, the TFCC was released, and the IOM distal up to and including the CB was released (one-way repeated-measures analysis of variance, 95% CI). Release of the CB in addition to the distal IOM and TFCC resulted in an average proximal migration of the radius of 6.8 mm in the position of neutral forearm rotation. In 4 of 6 specimens, the remaining proximal IOM was capable of preventing proximal migration of the radial stump to the capitellum. However, in 2 of 6 specimens, the proximal IOM was of insufficient substance to prevent complete migration of the radius. In these specimens, the remaining proximal IOM tore, resulting in abutment of the radial stump on the capitellum. Grafting
Reconstruction of the CB with the FCR autograft was successful in preventing complete migration of the radius to the capitellum; however, it was not capable of completely restoring the longitudinal stability of the forearm. Results of our grafting procedure are presented in Tables 3 and 4 for groups A and B, respectively. In group A, the graft was able to statistically restore the radius to a position consistent with an intact TFCC after all components of the IOM were released. In group B, the graft returned the radius to a position consistent with an intact proximal IOM but, with complete release of the CB, the distal IOM and TFCC. The graft effectively transferred load to the ulna, preventing complete proximal migration of the radius. Instability, indicated by greater proximal migration of the radius seen in the pronated position, was thought to be secondary to subluxation of the radial stump encouraged by the action of the pronator teres.
Discussion Instability of the DRUJ seen acutely with the Essex-Lopresti injury can be a difficult and perplex-
The Journal of Hand Surgery / Vol, 22A No. 6 November 1997
991
2-
PROXIMAL/DISTAL 1 LOCATION OF THE LUNATE FOSSA OF THE RADIUS WITH 0. RESPECT TO THE ULNAR DOME (ram) -1-
INTACT RADIAL HEAD EXCISED
-2-
-3
SUPINATION
FOREARMROTATION (deg)
PRONATION
Figure 3, Average changes in the proximal/distal location of the lunate fossa of the radius relative to the ulnar head. A positive displacement corresponds to a distal displacement of the radius with respect to the ulna. The lunate fossa of the radius was proximal to the ulnar head in pronation, which means that the ulnar head had a relatively more positive ulnar variance. Excision of the radial head caused proximal migration of the radius.
ing injury to treat. It is presumed that this injury includes fracture of the radial head, disruption of the IOM, and disruption of the TFCC. In other words, global instability of the forearm is present. This instability includes an axial component, manifested by proximal migration of the radius, DRUJ instability with dorsal/palmar subluxation or dislocation, and a radioulnar component with diastasis seen at the DRUJ and throughout the forearm. Optimal treatment of this complex injury cannot result without each component of this injury being addressed. Our previous article7 defined the anatomy of the IOM and, in particular, the anatomy of the CB. The CB has the appearance and consistency of a ligament; however, its biomechanical function has been poorly understood. This study has shown the CB to be a major stabilizing structure of the forearm. Strain response to physiologic loading is predictable, consistent, and dependent on the position of forearm rotation. Our data indicate that peak strain in the CB occurs in a position of pronation, not supination. This finding was surprising because visual inspection of the dissected IOM would suggest that the fibers of the CB were tightest in full supination, when the radius and ulna are parallel. In the laboratory, the CB attempts to resist proximal migration of the radius by transfer of load to the ulna. The unique arrangement of fibers seem to be maximally stressed in pronation. This finding is consistent with the fact that axial force transmitted to the
radiohumeral joint is greatest in a position of pronation30 Interestingly, this observation holds true even after the radial head has been excised. Radial head excision markedly increased the strain experienced by the CB, but maximum strain still occurs in a position of pronation. The normal response of the forearm to physiologic load at the wrist is therefore dependent on the CB. This biomechanical observation must be taken into account when considering CB reconstruction to restore axial stability to the forearm. Anatomically, the position of the lunate fossa of the radius with respect to the ulnar head is most distal in full supination and most proximal in full pronation. This relative ulnar positivity seen in pronation occurs as the radius crosses over the ulna, as it rotates around the fixed ulna. This finding correlates with radiologic measurements of ulnar variance in various forearm positions. 1~ This increased ulnar positivity trend in pronation is preserved after the radial head has been excised and the TFCC has been released. The orientation of the fibers in the IOM maintains the relative position of the radius to the ulna during forearm rotation. Axial stability of the forearm is likely dependent on a two-constraint system. The radial head serves as the primary restraint to proximal migration of the radius. The IOM and TFCC can be thought of as secondary restraints, serving to transfer load to the ulna by their fibers. Once the radial head is lost, the IOM and TFCC suddenly are called upon to serve as primary restraints. If these structures are competent,
992
Skahen et al. / Interosseous M e m b r a n e : Central Band Repair 15-.. , INT~,CT
t0--.
~.IWlTH C2 CUT WITH GRAFT TENSIONED
~1 CUT
\ \ 0-.
~.....................................i........~ . ~ ...... i~,
WITH C3 CUT
-5 WITH ALL CUT
-10-RADIUS -15/
i
-20
Figure 4. A coronal view of part of the distal radius and ulna with the forearm in neutral forearm rotation. Seven crosssectional views of the distal radius are shown, corresponding to how much the stabilizing structures of the forearm are sectioned. In this forearm, from group A, the order of sectioning was excision of the radial head (RH), excision of the proximal interosseous membrane (IOM) from the elbow joint up to but not including the central band (C1), excision of the central band (C2), excision of the distal IOM from the central band to the sigmoid notch (C3), and then excision of the triangular fibrocartilage complex (all cut). Here, large proximal migration of the radius occurs with sectioning of the last stabilizing structure. Central band reconstruction (graft) restores some of the axial position of the radius.
they can resist proximal migration of the radius. In our series, statistically significant proximal migration of the radius in neutral forearm rotation and in supination did not result with release of soft tissue structures from proximal to distal (group A) until the
entire I O M was released. In pronation, significant migration occurred before all the I O M was sectioned. Migration of the radius to the capitellum did not result until both the IOM and TFCC were released. In group B specimens, the CB and proxi-
Table 3. Location of the Lunate Fossa of the Radius With Respect to the Ulnar Dome at Various Forearm Rotation Positions* Location of Lunate Fossa in Millimeters (SD)t Condition
Neutral
Pronation
Supination
Intact Radial head removed Excision of the proximal IOM from the elbow joint up to but not including the CB Sectioning of the CB Sectioning of the distal IOM from the CB to the sigmoid notch Sectioning of the triangular fibrocartilage complex After CB reconstruction
1.1 (2.0) 0.6 (1.9) 1.0 (2.3)
-3.0 (3.7) -3.6 (4.3) -3.7 (4.5)
1.5 (1.3) 0.3 (0.9) 0.2 (1.1)
-0.8 (1.9) -2.2 (1.5)$
-4.7 (3.3) -5.9 (3.7)~:
-9,0 (3.6)$
-15.1 (4.4):[:
-2.0 (4.7)~:
-7.1 (6.1)$
-1.6 (1.7)$ -3.1 (1.7):~ -10.4 (2.6)~ -2.1 (4.2):~
* First set of fresh limbs (n = 6), with serial soft tissue release from proximal to distal. t Distal to ulnar dome is positive. ~: Statistical proximal migration of the radius compared to intact position. CB, central band; IOM, interosseous membrane.
The Journal of Hand Surgery / Vol. 22A No. 6 November 1997
993
. . . . . . . . . . . .. .. .. . . . . . .f........ . . . . . . . . . . .
-2o
..................................
,,,~o
/
-25
i
Figure 5. A coronal view of part of the distal radius and ulna with the forearm in neutral rotation. Seven cross-sectional views of the distal radius are shown corresponding to how much the stabilizing structures of the forearm are sectioned. In this forearm, from group B, the order of sectioning was excision of the radial head (RH), excision of the triangular fibrocartilage complex (C 1), excision of the distal interosseous membrane (IOM) from the wrist down to but not including the central band (C2), excision of the central band (C3), and then excision of the proximal IOM from the central band down to the elbow (all cut). Large radial migration occurs with sectioning of the last 2 structures. In this forearm, restoration of radial height following central band reconstruction (graft) was greater than the average shown in Table 4.
mal I O M were sufficient to prevent migration w h e n the m o r e distal structures had been released. Hence, both the C B and T F C C are important to the axial stability o f the forearm.
Mikid and Vukadinovid 12 reviewed the late results o f radial head excision in 60 patients for isolated fracture o f the radial head. Proximal migration o f the radius was present in 4 7 % and s y m p t o m a t i c subluxa-
Table 4. Location of the Lunate Fossa of the Radius With Respect to the Ulnar Dome at Various Forearm Rotation Positions* Location of Lunate Fossa in Millimeters (SD)~ Condition
Intact Radial head removed Sectioning of the triangular fibrocartilage complex Sectioning of the distal IOM from the wrist down to but not including the CB Sectioning of the CB Sectioning of the proximal IOM from the central band down to the elbow~: After CB reconstruction
Neutral
Pronation
Supination
-0.4 (1.5) -1.5 (1.3) -1.6 (1.2)
-3.0 (1.3) -4.0 (1.4) -4.5 (1.3)
1.0 (1.8) -0.1 (1.6) -0.2 (1.5)
-1.8 (1.3)
-4.9 (1.3)
-0.6 (1.7)
-7.2 (4.2)w -12.2 (2.3)w
- 11.3 (5.3)w -16.2 (2.4)w
-5.7 (4.7)w -12.1 (2.5)w
-5.9 (3.3)w
-10.6 (2.3)w
-4.9 (2.4)w
* Second set of fresh limbs (n = 6), with serial soft tissue release from distal to proximal. ? Distal to ulnar dome is positive. $ Here, n = 4 because in 2 arms, after sectioning the central band, the remainder of the IOC tore. w Statistical proximal migration of the radius compared to intact position. CB, central band; IOM, interosseous membrane.
994
Skahen et al. / Interosseous Membrane: Central Band Repair
tion of the DRUJ was present in 25%. The earliest presentation of these symptoms was 1 year after surgery. It seems possible that in certain patients, the IOM attenuates and fails over time, secondary to chronic force overload. This theory is supported by our data demonstrating a marked increase in strain experienced by the CB after radial head excision. Our biomechanical and anatomic observations of the IOM helped us to devise the described technique for CB reconstruction. We elected to reconstruct the CB of the IOM because this structure was the only anatomic component consistently found in each specimen. Biomechanical data indicated that the CB served to transfer load from the radius to the ulna through its fibers. This load transfer was markedly increased after radial head excision. The intricate fiber pattern of the origin and insertion of the CB would be difficult to accurately recreate surgically, so we elected to place the graft in the general direction of the native fiber orientation at the native sites of origin and insertion. Pilot studies in our laboratory found that the palmaris longus tendon, or only one half of the FCR tendon, was of insufficient strength to support physiologic load. However, the complete FCR proved to be adequate. The goal of creating a graft capable of preventing proximal migration of the radius by load transfer to the ulna was achieved. We were able to prevent migration of the radius, but we were not able to completely restore axial stability to the forearm. This is due to the fact that forearm instability with the Essex-Lopresti injury is a multifactorial problem. Our reconstruction procedure addressed only a single component of this problem. Our biomechanical and clinical observations suggest that stability could be enhanced by repair of the TFCC. CB reconstruction as described here has not been performed in the clinical setting and thus is not advocated at this time. Further investigation of this
complex injury is required. It is our belief that the radial head is primarily responsible for axial stability of the forearm and should be preserved whenever possible. Procedures such as CB reconstruction may play a role in the surgical care of these complex injuries in the future.
References 1. Curr JF, Coe WA. Dislocation of the inferior radio-ulnar joint. Br J Surg 1946;34:74-77. 2. Essex-Lopresti E Fractures of the radial head with distal radio-ulnar dislocation. J Bone Joint Surg 1951;33B: 244-247. 3. Hotchkiss RN, An K-N, 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:256-261. 4. Moore TM, Lester DK, Sarmiento A. The stabilizing effect of soft-tissue constraints in artificial Galeazzi fractures. Clin Orthop 1985;194:189-194. 5. Rabinowitz RS, Light TR, Havey RM, et al. The role of the interosseous membrane and triangular fibrocartilage complex in forearm stability. J Hand Surg 1994;19A: 385-393. 6. Sellman DC, Seitz WH, Postak PD. Reconstructive strategies for radioulnar dissociation: a biomechanical study. J Orthop Trauma 1995;9:516-522. 7. Skahen JR III, Palmer AK, Werner FW, Fortino MD. The interosseous membrane of the forearm: anatomy and function. J Hand Surg 1997;22A:981-985. 8. Palmer AK, Werner FW. Biomechanics of the distal radioulnar joint. Clin Orthop 1984; 187:26-35. 9. An K-N, Jaconsen MC, Berglund LJ, Cbao EYS. Application of a magnetic tracking device to kinesiologic studies. J Biomech 1988;21:613-621. 10. Morrey BF, An KN, Stormont TJ. Force transmission through the radial head. J Bone Joint Surg 1988;70A: 250-256. 11. Palmer AK, Glisson RR, Werner FW. Ulnar variance determination. J Hand Surg 1982;7:376-379. 12. Miki6 ZD, Vukadinovi6 SM. Late results in fractures of the radial head treated by excision. Clin Or*hop 1983;181: 220-228.
Fracture of the radial head with dislocation of the distal radioulnar joint (DRUJ) was first described by Curr and Coe in 1946. 2 It was not until 1951 that this injury received more widespread recognition, and it has since been known as the Essex-Lopresti lesion. 2 EssexLopresti believed that this injury must also include disruption of the interosseous membrane (IOM) of the forearm. In the last 2 decades, authors have suggested that this injury might also include disruption of the triangular fibrocartilage complex (TFCC). 3~
From the Department of Orthopedic Surgery, State University of NewYorkHealthScienceCenter, Syracuse,NY. Funded in part by a grant from the AmericanSocietyfor Surgeryof the Hand. Received forpublicationMarch 19, 1996; acceptedin revised form April 16, 1997. No benefitsin any formhave been receivedor will be receivedfroma commercialpartyrelateddirectlyor indirectlyto the subjectof this article. Reprint requests: FrederickW. Werner,MME, Departmentof Orthopedic Surgery, SUNY Health Science Center, 750 E. Adams Street, Syracuse,NY 13210.
986
The Journal of Hand Surgery
Proximal migration of the radius after resection of the radial head in the treatment o f the EssexLopresti lesion can result in pain and disability o f the DRUJ. It is also possible that proximal migration of the radius after radial head excision can occur over time as the IOM attenuates and fails secondary to chronic force overload. Resection of the radial head alone can exacerbate this problem and should be avoided if at all possible. Current surgical approaches to this problem include resection o f the radial head and pinning o f the DRUJ until the soft tissues have healed, silicone arthroplasty of the proximal radius, and creation of a single-bone forearm. Results o f these procedures are inconsistent and fail to address the entire problem. Sellman et al. investigated reconstructive strategies for radioulnar dissociation from a biomechanical perspective using silicone and titanium implants with and without a braided polyester cord substitute for the central band (CB) of the IOM: they obtained variable results. 6
The Journal of Hand Surgery / Vol. 22A No. 6 November 1997
In an earlier article, we described the anatomy of the IOM of the forearm in detail. 7 We demonstrated that when the radial head is lost, the CB of the IOM resists proximal migration of the radius, by transferring load to the ulna. Theoretically in an EssexLopresti lesion, reconstruction of a damaged IOM of the forearm with a load-sharing graft might prevent proximal migration of the radius. Such a procedure might serve to improve the long-term outcome of this difficult injury. The first goal of this study was to clarify the axial stabilizing roles of the forearm, specifically the TFCC and the IOM. The second goal was to develop a surgical protocol that would restore axial stability after an Essex-Lopresti injury by providing a graft capable of transferring load from the radius to the ulna, thus preventing proximal migration of the radius.
Materials and Methods Biomechanics
Twelve fresh-frozen upper extremities were studied. Each specimen was transected at the junction of the middle and distal thirds of the humerus. All specimens were dissected free of investing soft tissues, leaving the structures of the hand, wrist, IOM, and elbow intact. The extensor carpi radialis brevis, extensor carpi radialis longus, extensor carpi ulnaris, flexor carpi ulnaris, and flexor carpi radialis (FCR) tendons were preserved for physiologic loading of the wrist and forearm. The tendons of the pronator teres and biceps were also preserved to allow dynamic pronation and supination by alternate manual loading of these tendons. A customized mounting frame was designed to hold each specimen in a standard position. The forearm was maintained in a vertical position. The ulnohumeral joint was pinned at 90~ the radiohumeral joint was left free to pronate and supinate. The wrist was maintained in 0 ~ of extension by means of a 1.58-mm (0.062-inch) Steinmann pin placed in the medullary canal of the middle finger metacarpal. This pin also permitted unconstrained forearm rotation around the fixed ulna. A large intermedullary pin was cemented into the humeral stump of each specimen, serving to anchor each specimen to the testing frame. Loading of the forearm and wrist was done by applying 22.2 N (5 lb.) of load to each of the primary wrist motors, for a total of 89 N applied across the wrist. 8 A differential voltage reluctance transducer ([DVRT] MicroStrain, Inc, Burlington, VT) was embedded in
987
the midsubstance of the CB on each specimen, as in our previous study. 7 This small displacement transducer allowed us to calculate the strain in the CB during physiologic loading. The displacement data, later converted to strain, were recorded at a rate of 10 Hz. A 3 Space electromagnetic tracking system ~0 was also used in this study. Sensors were mounted on the dorsal surface of the distal ulna and radius. Their three-dimensional angular and translation locations with respect to the reference source were recorded throughout the experiment by computer acquisition of data. These measurements were synchronized with the strain measurement data and recorded simultaneously. This system allowed an accurate and reproducible three-dimensional record of the position of the radius and ulna throughout the experiment. At the conclusion of the experiment, the articulating surfaces and coronal outlines of the distal radius and ulna were digitized using this same system and recorded relative to the electromagnetic source. Mathematic transformation of the data then permitted us to determine the three-dimensional location of the distal articulating surfaces of the radius, at any supination and pronation position, relative to the ulna. Strain in the CB was recorded during dynamic pronation and supination. Each of the 12 specimens was tested in the intact state and then again after the radial head was excised. Zero strain was defined in a stationary neutral forearm rotation in the intact specimen with the physiologic load applied. To analyze the relative contribution of the IOM of the forearm and the TFCC to the axial stability of the forearm, we divided the specimens into 2 groups of 6 each. The motions of the radius and ulna along with the strain in the CB were recorded during dynamic forearm rotation as the IOM and the TFCC were serially divided. The motion data of the radius and ulna were used to compute the relative position of the lunate fossa of the radius with respect to the head of the ulna. In group A, the order of sectioning was proximal to distal. Measurements were first made with the forearm intact, then after radial head excision, after sectioning of the IOM proximal to but not including the CB, after sectioning of the CB, after sectioning of the distal IOM, and finally after sectioning of the TFCC. In group B, the order of sectioning was distal to proximal. Measurements were first made with the forearm intact, after radial head excision, after sectioning of the TFCC, after sectioning of the distal IOM up to but not including
988
Skahen et al. / Interosseous Membrane: Central Band Repair
the CB, after sectioning of the CB, and finally after sectioning of the proximal IOM.
Central Band Reconstruction Our anatomic study v of the IOM of the forearm demonstrated that the CB was the most dominant and consistent structure. The biomechanical data indicated that the CB experienced strain in a dynamic fashion, dependent on forearm rotation. 8 In addition, radial head excision dramatically increased the strain experienced by the CB. On the basis of this information, we developed a surgical protocol for the reconstruction of the CB. Our goal was to restore axial stability to the forearm after an Essex-Lopresti injury by providing a graft capable of transferring load from the radius to the ulna, thus preventing proximal migration of the radius. A reconstructive procedure was performed in each of the 12 fresh forearms after serial sectioning of the TFCC and IOC. It was believed that after these sectionings, each specimen had in essence an EssexLopresti injury. First, the DRUJ of each specimen was pinned in neutral forearm rotation, in the position of ulnar variance native to each specimen. The original native ulnar variance of each specimen had been recorded before starting the experiment. A neutral forearm rotation position was chosen, since in the intact specimen this position produces strain in the CB that is generally midway between maximum and minimum strain. In addition, we found that maximum tensioning of the graft in full pronation severely limited supination, and tended to force the radius distally. The FCR was harvested from each specimen during initial preparation. Our preliminary studies found that the palmaris longus and only one half of the FCR were inadequate as graft material. They were unable to support the radius under physiologic loading. For this reason, the full FCR tendon was used for grafting purposes. The origin and insertion of the CB of each specimen was identified in the intact specimen with a surgical marker prior to the start of the biomechanical study. Graft length was then directly measured in the direction of the fibers of the CB and the FCR was cut to length. Our goal was to place the graft in the position and orientation of the native CB for each specimen. To anchor the graft within the substance of the radius and ulna, a 6.35-mm (1/4-inch) diameter drill hole was placed in the radius and ulna at the points of origin and insertion. These holes were placed in the coronal plane and directed to the orientation of the native CB fibers.
The ends of the FCR autograft were then secured with #5 nonabsorbable braided polyester suture, with a standard whipstitch used to prevent pullout. A suture passer was then used to pass the graft, through the previously drilled holes, from the radius to the ulna. The radial limb of the graft was then secured to the radial cortex of the radius by tying the suture over a nylon button. The graft was then maximally tensioned by pulling the sutures in the ulnar limb of the graft. The ulnar limb of the graft was then tied over a nylon button. Figure 1 illustrates the grafting procedure. During the entire reconstructive procedure, native ulnar variance was maintained by a pin in the DRUJ. In addition, each specimen was reconstructed with the forearm in the unloaded state. No attempt to repair the TFCC was made in this study.
Results Strain in the Central Band of the Interosseous Membrane Figure 2 illustrates the strain experienced by the CB under physiologic loading as the forearm is dynamically rotated from pronation to supination. Since this graph represents the average data from 11 specimens, it only spans the range in supination and pronation common to all 11. A single specimen was deleted from this analysis because of accidental displacement of the DVRT barbs during experimentation, and data salvage was not possible. In the intact specimens, strain in the CB was the least in full supination and it progressively increased to a maximum in full pronation. This relationship was not dependent on direction of rotation, as data taken during full supination to full pronation demonstrated the same trend. Excision of the radial head did not change this relationship; rather, the strain in the CB was universally greater throughout forearm rotation. This increase in strain after radial head excision was statistically significant from full pronation to 36 ~ of supination (one-tailed paired t-test, p < .05). Table 1 represents strains in the CB for specimens in group A (soft tissue release from proximal to distal) at the neutral forearm rotation position. Simple excision of the radial head resulted in a 0.67% increase in strain. Release of the proximal IOM from the elbow up to but not including the CB caused an increase of 1.64%. In a pilot study, we have shown that a force of 50 N applied directly to the CB can cause a 1% increase in strain in the CB, suggesting that these strain levels are not trivial. Similar data for group B (soft tissue release from distal to proximal) are presented in Table 2. Removal
The Journal of Hand Surgery/ Vol. 22A No. 6 November 1997 989
Figure 1. A reconstructive graft for the central band of the interosseous membrane. Flexor carpi radialis (FCR) autograft is secured in the position and orientation of the original central band. Each end of the FCR is held with #5 nonabsorbable braided polyester suture using a whipstitch, passed through oblique holes in the radius and ulna, maximally tensioned, and tied to a nylon button. The ulna is on the left, the radius is on the right, and distal is at the top.
of the radial head in the loaded specimen resulted in an increase in strain comparable to that in group A. Whereas excision of the T F C C did not alter the strain in the CB, release of the I O M from the wrist up to but not including the CB resulted in an increased strain of 1.37%.
Proximal Migration of the Radius The location of the lunate fossa of the radius with respect to the position of the ulnar head was computed from the data recorded throughout the experiment with the 3 Space tracking system. In the intact
1-
o., f _ _ : _ 0.8
% STRAIN 0.4 IN CB 0"2 0
"0"2t -0.4
.5o
-,io
SUPINATION
-1'o
o
1'o
FOREARMROTATION (deg)
2'0
3'0
4'o
PRONATION
Figure 2. Average changes in the strain in the central band (CB) under physiologic loading as the forearm was dynamically rotated from pronation to supination. Strain was greatest in pronation and increased with excision of the radial head. The increase in strain with radial head excision was statistically significant from full pronation to 36 ~ of supination.
990
Skahen et al. / Interosseous Membrane: Central Band Repair
Table 1. Percent Strain in the Interosseous Membrane Central Band at 0~ of Forearm Rotation for First Set of Fresh Limbs (n = 4), With Serial Soft Tissue Release From Proximal to Distal* % Strain (SD)
Intact forearm Radial head removed Excision of the proximal interosseous membrane from the elbowjoint up to but not includingthe central band
-0.06 (0.19) 0.67 (0.42) 1.64 (0.99)
* Data availablefrom only 4 specimens, since strain data were not initially recorded with partial excision of the interosseous membranein all specimens.
specimen, the position of the lunate fossa of the radius is most distal in full supination and most proximal in full pronation. This relationship is maintained even after the radial head has been removed. Figure 3 represents the average proximal migration of the lunate fossa of the radius for the 12 specimens. The relative location of the lunate fossa of the radius to the ulnar head is given in Table 3 and Figure 4 for the group A specimens. The average of all 6 specimens is given in Table 3 for 3 static positions: neutral forearm rotation, full pronation, and full supination. Figure 4 shows a coronal view of the distal radius and ulna for 1 specimen at neutral forearm rotation. In supination, statistically significant (oneway repeated-measures analysis of variance, 95% confidence interval [CI]) proximal migration of the radius occurred after the radial head was excised and the proximal and CB regions of the IOM were sectioned. In neutral and pronation, significant migration occurred only after the distal portion of the IOM had been sectioned as well. Complete proximal migration of the radius to the point where the stump abutted the capitellum occurred only after complete release of the IOM and the TFCC. The apparent increased proximal migration of the radius in the
Table 2. Percent Strain in the Interosseous Membrane Central Band at 0 ~ of Forearm Rotation for Second Set of Fresh Limbs (n = 6), With Serial Soft Tissue Release From Distal to Proximal % Strain (SD)
Intact forearm Radial head removed Triangular fibrocartilagecomplex excised Excision of the distal interosseousmembrane from the wrist up to but not includingthe central band
0.08 (0.22) 0.59 (0.69) 0.54 (0.83) 1.37 (0.50)
pronated positions is due to anterior and medial displacement of the proximal radius, in turn caused by the action of the pronator teres in a grossly unstable forearm. In other words, the proximal radius was no longer in contact with the capitellum and was therefore free to migrate to a more proximal position. The relative position of the lunate fossa of the radius with respect to the ulnar head for group B specimens is presented in Table 4 and Figure 5. Table 4 represents the average data for the 6 specimens, in the 3 specified static positions. Statistically significant proximal migration of the radius did not occur until the radial head was excised, the TFCC was released, and the IOM distal up to and including the CB was released (one-way repeated-measures analysis of variance, 95% CI). Release of the CB in addition to the distal IOM and TFCC resulted in an average proximal migration of the radius of 6.8 mm in the position of neutral forearm rotation. In 4 of 6 specimens, the remaining proximal IOM was capable of preventing proximal migration of the radial stump to the capitellum. However, in 2 of 6 specimens, the proximal IOM was of insufficient substance to prevent complete migration of the radius. In these specimens, the remaining proximal IOM tore, resulting in abutment of the radial stump on the capitellum. Grafting
Reconstruction of the CB with the FCR autograft was successful in preventing complete migration of the radius to the capitellum; however, it was not capable of completely restoring the longitudinal stability of the forearm. Results of our grafting procedure are presented in Tables 3 and 4 for groups A and B, respectively. In group A, the graft was able to statistically restore the radius to a position consistent with an intact TFCC after all components of the IOM were released. In group B, the graft returned the radius to a position consistent with an intact proximal IOM but, with complete release of the CB, the distal IOM and TFCC. The graft effectively transferred load to the ulna, preventing complete proximal migration of the radius. Instability, indicated by greater proximal migration of the radius seen in the pronated position, was thought to be secondary to subluxation of the radial stump encouraged by the action of the pronator teres.
Discussion Instability of the DRUJ seen acutely with the Essex-Lopresti injury can be a difficult and perplex-
The Journal of Hand Surgery / Vol, 22A No. 6 November 1997
991
2-
PROXIMAL/DISTAL 1 LOCATION OF THE LUNATE FOSSA OF THE RADIUS WITH 0. RESPECT TO THE ULNAR DOME (ram) -1-
INTACT RADIAL HEAD EXCISED
-2-
-3
SUPINATION
FOREARMROTATION (deg)
PRONATION
Figure 3, Average changes in the proximal/distal location of the lunate fossa of the radius relative to the ulnar head. A positive displacement corresponds to a distal displacement of the radius with respect to the ulna. The lunate fossa of the radius was proximal to the ulnar head in pronation, which means that the ulnar head had a relatively more positive ulnar variance. Excision of the radial head caused proximal migration of the radius.
ing injury to treat. It is presumed that this injury includes fracture of the radial head, disruption of the IOM, and disruption of the TFCC. In other words, global instability of the forearm is present. This instability includes an axial component, manifested by proximal migration of the radius, DRUJ instability with dorsal/palmar subluxation or dislocation, and a radioulnar component with diastasis seen at the DRUJ and throughout the forearm. Optimal treatment of this complex injury cannot result without each component of this injury being addressed. Our previous article7 defined the anatomy of the IOM and, in particular, the anatomy of the CB. The CB has the appearance and consistency of a ligament; however, its biomechanical function has been poorly understood. This study has shown the CB to be a major stabilizing structure of the forearm. Strain response to physiologic loading is predictable, consistent, and dependent on the position of forearm rotation. Our data indicate that peak strain in the CB occurs in a position of pronation, not supination. This finding was surprising because visual inspection of the dissected IOM would suggest that the fibers of the CB were tightest in full supination, when the radius and ulna are parallel. In the laboratory, the CB attempts to resist proximal migration of the radius by transfer of load to the ulna. The unique arrangement of fibers seem to be maximally stressed in pronation. This finding is consistent with the fact that axial force transmitted to the
radiohumeral joint is greatest in a position of pronation30 Interestingly, this observation holds true even after the radial head has been excised. Radial head excision markedly increased the strain experienced by the CB, but maximum strain still occurs in a position of pronation. The normal response of the forearm to physiologic load at the wrist is therefore dependent on the CB. This biomechanical observation must be taken into account when considering CB reconstruction to restore axial stability to the forearm. Anatomically, the position of the lunate fossa of the radius with respect to the ulnar head is most distal in full supination and most proximal in full pronation. This relative ulnar positivity seen in pronation occurs as the radius crosses over the ulna, as it rotates around the fixed ulna. This finding correlates with radiologic measurements of ulnar variance in various forearm positions. 1~ This increased ulnar positivity trend in pronation is preserved after the radial head has been excised and the TFCC has been released. The orientation of the fibers in the IOM maintains the relative position of the radius to the ulna during forearm rotation. Axial stability of the forearm is likely dependent on a two-constraint system. The radial head serves as the primary restraint to proximal migration of the radius. The IOM and TFCC can be thought of as secondary restraints, serving to transfer load to the ulna by their fibers. Once the radial head is lost, the IOM and TFCC suddenly are called upon to serve as primary restraints. If these structures are competent,
992
Skahen et al. / Interosseous M e m b r a n e : Central Band Repair 15-.. , INT~,CT
t0--.
~.IWlTH C2 CUT WITH GRAFT TENSIONED
~1 CUT
\ \ 0-.
~.....................................i........~ . ~ ...... i~,
WITH C3 CUT
-5 WITH ALL CUT
-10-RADIUS -15/
i
-20
Figure 4. A coronal view of part of the distal radius and ulna with the forearm in neutral forearm rotation. Seven crosssectional views of the distal radius are shown, corresponding to how much the stabilizing structures of the forearm are sectioned. In this forearm, from group A, the order of sectioning was excision of the radial head (RH), excision of the proximal interosseous membrane (IOM) from the elbow joint up to but not including the central band (C1), excision of the central band (C2), excision of the distal IOM from the central band to the sigmoid notch (C3), and then excision of the triangular fibrocartilage complex (all cut). Here, large proximal migration of the radius occurs with sectioning of the last stabilizing structure. Central band reconstruction (graft) restores some of the axial position of the radius.
they can resist proximal migration of the radius. In our series, statistically significant proximal migration of the radius in neutral forearm rotation and in supination did not result with release of soft tissue structures from proximal to distal (group A) until the
entire I O M was released. In pronation, significant migration occurred before all the I O M was sectioned. Migration of the radius to the capitellum did not result until both the IOM and TFCC were released. In group B specimens, the CB and proxi-
Table 3. Location of the Lunate Fossa of the Radius With Respect to the Ulnar Dome at Various Forearm Rotation Positions* Location of Lunate Fossa in Millimeters (SD)t Condition
Neutral
Pronation
Supination
Intact Radial head removed Excision of the proximal IOM from the elbow joint up to but not including the CB Sectioning of the CB Sectioning of the distal IOM from the CB to the sigmoid notch Sectioning of the triangular fibrocartilage complex After CB reconstruction
1.1 (2.0) 0.6 (1.9) 1.0 (2.3)
-3.0 (3.7) -3.6 (4.3) -3.7 (4.5)
1.5 (1.3) 0.3 (0.9) 0.2 (1.1)
-0.8 (1.9) -2.2 (1.5)$
-4.7 (3.3) -5.9 (3.7)~:
-9,0 (3.6)$
-15.1 (4.4):[:
-2.0 (4.7)~:
-7.1 (6.1)$
-1.6 (1.7)$ -3.1 (1.7):~ -10.4 (2.6)~ -2.1 (4.2):~
* First set of fresh limbs (n = 6), with serial soft tissue release from proximal to distal. t Distal to ulnar dome is positive. ~: Statistical proximal migration of the radius compared to intact position. CB, central band; IOM, interosseous membrane.
The Journal of Hand Surgery / Vol. 22A No. 6 November 1997
993
. . . . . . . . . . . .. .. .. . . . . . .f........ . . . . . . . . . . .
-2o
..................................
,,,~o
/
-25
i
Figure 5. A coronal view of part of the distal radius and ulna with the forearm in neutral rotation. Seven cross-sectional views of the distal radius are shown corresponding to how much the stabilizing structures of the forearm are sectioned. In this forearm, from group B, the order of sectioning was excision of the radial head (RH), excision of the triangular fibrocartilage complex (C 1), excision of the distal interosseous membrane (IOM) from the wrist down to but not including the central band (C2), excision of the central band (C3), and then excision of the proximal IOM from the central band down to the elbow (all cut). Large radial migration occurs with sectioning of the last 2 structures. In this forearm, restoration of radial height following central band reconstruction (graft) was greater than the average shown in Table 4.
mal I O M were sufficient to prevent migration w h e n the m o r e distal structures had been released. Hence, both the C B and T F C C are important to the axial stability o f the forearm.
Mikid and Vukadinovid 12 reviewed the late results o f radial head excision in 60 patients for isolated fracture o f the radial head. Proximal migration o f the radius was present in 4 7 % and s y m p t o m a t i c subluxa-
Table 4. Location of the Lunate Fossa of the Radius With Respect to the Ulnar Dome at Various Forearm Rotation Positions* Location of Lunate Fossa in Millimeters (SD)~ Condition
Intact Radial head removed Sectioning of the triangular fibrocartilage complex Sectioning of the distal IOM from the wrist down to but not including the CB Sectioning of the CB Sectioning of the proximal IOM from the central band down to the elbow~: After CB reconstruction
Neutral
Pronation
Supination
-0.4 (1.5) -1.5 (1.3) -1.6 (1.2)
-3.0 (1.3) -4.0 (1.4) -4.5 (1.3)
1.0 (1.8) -0.1 (1.6) -0.2 (1.5)
-1.8 (1.3)
-4.9 (1.3)
-0.6 (1.7)
-7.2 (4.2)w -12.2 (2.3)w
- 11.3 (5.3)w -16.2 (2.4)w
-5.7 (4.7)w -12.1 (2.5)w
-5.9 (3.3)w
-10.6 (2.3)w
-4.9 (2.4)w
* Second set of fresh limbs (n = 6), with serial soft tissue release from distal to proximal. ? Distal to ulnar dome is positive. $ Here, n = 4 because in 2 arms, after sectioning the central band, the remainder of the IOC tore. w Statistical proximal migration of the radius compared to intact position. CB, central band; IOM, interosseous membrane.
994
Skahen et al. / Interosseous Membrane: Central Band Repair
tion of the DRUJ was present in 25%. The earliest presentation of these symptoms was 1 year after surgery. It seems possible that in certain patients, the IOM attenuates and fails over time, secondary to chronic force overload. This theory is supported by our data demonstrating a marked increase in strain experienced by the CB after radial head excision. Our biomechanical and anatomic observations of the IOM helped us to devise the described technique for CB reconstruction. We elected to reconstruct the CB of the IOM because this structure was the only anatomic component consistently found in each specimen. Biomechanical data indicated that the CB served to transfer load from the radius to the ulna through its fibers. This load transfer was markedly increased after radial head excision. The intricate fiber pattern of the origin and insertion of the CB would be difficult to accurately recreate surgically, so we elected to place the graft in the general direction of the native fiber orientation at the native sites of origin and insertion. Pilot studies in our laboratory found that the palmaris longus tendon, or only one half of the FCR tendon, was of insufficient strength to support physiologic load. However, the complete FCR proved to be adequate. The goal of creating a graft capable of preventing proximal migration of the radius by load transfer to the ulna was achieved. We were able to prevent migration of the radius, but we were not able to completely restore axial stability to the forearm. This is due to the fact that forearm instability with the Essex-Lopresti injury is a multifactorial problem. Our reconstruction procedure addressed only a single component of this problem. Our biomechanical and clinical observations suggest that stability could be enhanced by repair of the TFCC. CB reconstruction as described here has not been performed in the clinical setting and thus is not advocated at this time. Further investigation of this
complex injury is required. It is our belief that the radial head is primarily responsible for axial stability of the forearm and should be preserved whenever possible. Procedures such as CB reconstruction may play a role in the surgical care of these complex injuries in the future.
References 1. Curr JF, Coe WA. Dislocation of the inferior radio-ulnar joint. Br J Surg 1946;34:74-77. 2. Essex-Lopresti E Fractures of the radial head with distal radio-ulnar dislocation. J Bone Joint Surg 1951;33B: 244-247. 3. Hotchkiss RN, An K-N, 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:256-261. 4. Moore TM, Lester DK, Sarmiento A. The stabilizing effect of soft-tissue constraints in artificial Galeazzi fractures. Clin Orthop 1985;194:189-194. 5. Rabinowitz RS, Light TR, Havey RM, et al. The role of the interosseous membrane and triangular fibrocartilage complex in forearm stability. J Hand Surg 1994;19A: 385-393. 6. Sellman DC, Seitz WH, Postak PD. Reconstructive strategies for radioulnar dissociation: a biomechanical study. J Orthop Trauma 1995;9:516-522. 7. Skahen JR III, Palmer AK, Werner FW, Fortino MD. The interosseous membrane of the forearm: anatomy and function. J Hand Surg 1997;22A:981-985. 8. Palmer AK, Werner FW. Biomechanics of the distal radioulnar joint. Clin Orthop 1984; 187:26-35. 9. An K-N, Jaconsen MC, Berglund LJ, Cbao EYS. Application of a magnetic tracking device to kinesiologic studies. J Biomech 1988;21:613-621. 10. Morrey BF, An KN, Stormont TJ. Force transmission through the radial head. J Bone Joint Surg 1988;70A: 250-256. 11. Palmer AK, Glisson RR, Werner FW. Ulnar variance determination. J Hand Surg 1982;7:376-379. 12. Miki6 ZD, Vukadinovi6 SM. Late results in fractures of the radial head treated by excision. Clin Or*hop 1983;181: 220-228.