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Biomechanical analysis of mallet finger fracture fixation techniques
Biomechanical analysis of mallet finger fracture fixation techniques A biomechanical fracture
study was conducted to determine the best fixation technique for mallet finger
among four commonly
biomechanical
used methods.
properties, and maintenance
Considerations
were technical complications,
of reduction. Techniques tested included Kirschner
wire, figure-of-eight wire, tension band wire, and tension band suture. Technical complications were frequent with both the Kirschner wire and tension band wire techniques.
Biomechanical
testing yielded significantly greater energy absorbed to failure and a trend toward greater peak loads to failure for both the figure-of-eight wire and tension band suture techniques. Irreversible loss of reduction during testing occurred in all of the Khschner of the tension band wire-&d No irreversible
wire-fixed
fractures,
fractures, and in 50% of the figure-of-eight wire-fixed
failure occurred in the tension band suture group. (J
HAND
in 60%
fractures.
SURC 1993;18A:
600-7.)
Timothy A. Damron, MD, William D. Engber, MD, Richard H. Lange, MD, Ron McCabe, BS, Leatha A. Damron, BS, Mark Ulm, MS, and Ray Vanderby, PhD, Madison, Wis .
N
o single treatment modality for mallet finger fractures has achieved consistently excellent results in terms of eliminating deformity, stiffness, arthritis, and complications. Treatment options include closed reduction with splinting and numerous techniques for open reduction and internal fixation (ORIF). Early reports support operative repair for dorsal fragments involving more than one third of the articular surface. I-3 However, more recent series suggest that open treatment be reserved for fractures that fail to reduce to a congruent articular arc without subluxation when splinted in extension.4-6 The retrospective review of a large number of mallet finger fractures by WehbC and Schneider’ has been cited
From Division of orthopedics and the Biomechanics Laboratory, Department of Surgery, University of Wisconsin, Madison, Wis. Received for publication 8, 1993.
April 2, 1992; accepted in revised form Jan.
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: William D. Engber, MD, G51322 Clinical Science Center, Division of Chthopedics, University of Wisconsin, 600 Highland Ave., Madison, WI 53792. 311146261
600
THE JOURNAL OF HAND SURGERY
as support for closed treatment of all such injuries, even those associated with subluxation or incongruency in the splint.s At final follow-up, residual pain, dorsal prominence, extensor lag, and degenerative changes were common problems .’ Their preference for splinting appears to be based more on their poor results with operative treatment than on excellent results with nonoperative treatment.’ In our experience, unreduced palmar subluxation is associated with poor outcomes4 Techniques for ORIF of mallet finger fractures have involved fragment fixation with suture, wire, or pins and/ or transarticular pins. ‘-‘a9-2o Reported complications include infection, nail deformity, joint incongruities, fixation/ hardware failure, and secondary deformities .*l In their clinical review of treatment complications, Stem and Kastrup” suggested that complication rates differ significantly between ORIF techniques. The composite of Kirschner (K-) wire fragment fixation and transarticular pinning, exactly the technique used by Wehbe and Schneider,’ was associated with the highest surgical complication rate. Pull-out wires with transarticular pin fixation yielded the lowest complication rate in the series reported by Stem and Kastrup . Despite the abundance of clinical studies, there have previously been no laboratory evaluations of mallet fin-
Vol. 18A, No. 4 July 1993
Mallet finger fracture @cation techniques
601
ger fracture fixation techniques. The purpose of this study was to determine the best technique among four commonly used methods. Fixation variables studied included the stability of fixation maintenance after loading and the frequency of technical problems associated with each technique. Materials and methods Ten fresh frozen hands were acquired from donors 47 to 70 years old with no history of chemotherapy, local radiotherapy, or prolonged steroid usage. Whole hands were procured within 12 hours after death and frozen at - 70” C. The hands were individually thawed to allow fracture simulation and fixation. The base of the distal phalanx was exposed on the index, long, ring, and small fingers; thumbs were not used. The nail was removed to avoid interference with the osteotomy cut. Reproducible fracture simulation was done by making an oblique dorsal cut at the base of the distal phalanx over a K-wire 0.027 inch in diameter by means of a 0.03 cm thick blade on a microsagittal saw under fluoroscopic control (Fig. 1, A). The osteotomy created a dorsal fragment involving an average of 45% (range, 29% to 60%) of the attic&u surface as measured on a true lateral fluoroscopic print of the cut digit. The extensor tendon insertion on this dorsal fragment was preserved. Fluorographic prints were made of each cut to document the size of the dorsal fragment (Fig. 1, B). Techniques were assigned among fingers in a randomized block fashion. Techniques tested included fixation with K-wires (KW),’ figure-of-eight wire (F8W),” tension band wire (TBW),** and tension band suture (TBS).** Only one technique was performed on each digit. All of the procedures were performed by one surgeon (T.A.D.). The KW technique was used in the fashion reported by WehbC and Schneider, directing two 0.035inch K-wires from dorsally and proximally through the dorsal fragment in a palmar and distal direction into the major portion of the distal phalanx.’ Fluoroscopic control was used to guide reduction and fixation. The wires were cut and left unbent after placement. The F8W technique followed the description by Jupiter and Sheppard. ‘* A 28-gauge stainless steel wire was directed beneath the tendon insertion, over the dorsal fragment, and through a transverse hole in the dorsal aspect of the major portion of the distal phalanx just distal to the osteotomy cut. The hole was created with a 21-gauge needle through which the wire was passed. The wire was tightened over the dorsal surface in a
Fig. 1. Technique for mallet fracture simulation and fixation by TBS. A, Pluorographic print negative lateral view of the DIP joint shows K-wire guide positioned in distal phalanx from dorsal-distal to an intra-articular position to serve as a guide for the cutting blade. B, Dorsal articular fragment of same specimen has been created by cutting along the K-wire guide with a microsagittal saw blade. C, Reduction and fixation of same specimen has been achieved with the TBS technique.
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Fig. 2. Technique for mallet fracture simulation and fixation by F8W. A, K-wire guide is in position, B, Dorsal articular fragment has been created. C, Reduction and fixation have been achieved with the F8W technique.
The Journal of HAND SURGERY
Fig. 3. Detailed operative technique for TBS and TBW. A, Placement of suture anterior to insertion of extensor with strands directed dorsally over fragment. B, Keith needles used to pass suture ends through distal phalanx. C, Dorsal view of reduced fracture with sutures pulled taut. D, Preparation for tying suture through button on palmar aspect. Clinically, a TeIfa pad is used beneath the button to protect the skin.
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Fig. 4. Testing apparatus. Amputated specimen is held in position by middle phalangeal intramedullary screw. Extensor tendon is pulled taut around capstan device. Loading device connected to ram on Bionix MTS 858 servohydraulic load frame is lowered into contact with distal phalanx just distal to osteotomy site. Central portion of loading device is scalloped (not shown) to avoid contact with middle phalanx during testing excursion. figure-of-eight
fashion
with a single limb twist (Fig.
2). Both the TBW and TBS procedures were performed in identical fashion, with the use of 28-gauge stainless steel wire for TBW and 2-O Supramid sutures (S. Jackson Inc., Alexandria, Va.) for TBS (Fig. 3).22 The tension band material was passed beneath the extensor tendon in the axilla between tendon insertion and bone of the dorsal fragment. The strands were then directed dorsally over the dorsal fragment through the dorsal epitenon. Two drill holes were created for these two strands, beginning just distal to the osteotomy site and directed palmarly and distally through the palmar skin of the finger. A 21-gauge needle was used to create the drill hole for passage of the wire, and a Keith needle was used for passage of the suture. The limbs were then pulled through and twisted or tied palmarly (Fig. 1, 0. Each specimen was amputated at the proximal interphalangeal joint, maintaining the attached extensor tendon, which was transected at its musculotendinous junction. The proximal intramedullary canal of the middle phalanx was drilled with a 2.0 mm drill and tapped with a 2.7 mm tap. The length, width, and depth of the specimens were measured with calipers. All biomechanical testing was done on a single day.
The middle phalanx was mounted rigidly to the testing device with a 2.7 mm cortical screw (Fig. 4). The extensor tendon was wrapped around a roughened capstan device that was tightened with a torque wrench to 12 inch-ounces to keep the distal interphalangeal joint (DIP) fully extended. The Bionix MTS 858 servohydraulic load frame (MTS, Minneapolis, Minn.) was then used to apply a flexion load just distal to the osteotomy over a 3 cm ramp excursion that lasted 2 seconds. Markings on the extensor tendon did not move relative to the grips during the testing, which confirmed the absence of loosening of the tendon on the capstan device. The end point of flexion was displacement at the osteotomy site in 90 degrees of flexion. Each finger was removed from the testing device and inspected closely for mode of failure. The extensor tendon was then pulled into full extension again, and fluorographic prints were obtained to document the extent of residual displacement. A load-deformation curve was plotted for each digit, from which stiffness, peak load, and energy to failure were derived. Statistical analysis was performed under the guidance of a statistician with the use of Statistical Analysis System (SAS) software. Analysis of variance (ANOVA) was performed to identify differences in numerical variables between technique groups. Fisher’s Exact Test
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Damron et al.
TBW TBS
KW
* P < 0.05 0 0
loo
for
3
4
STIFFNESS (N/mm)
ENERGY ABSORBED (N-mm) Fig. 5. Energy absorbed to failure in newton-millimeters each technique. Error bars signify standard error.
2
1
300
200
Fig. 7. Stiffness in newtons per millimeter for each technique. Error bars signify standard error.
TBW TBS TBS
* P = 0.0011
Q c
FSW
DirpsocslRnr orTerrden Tear
c
V
A
KW KW
0 0
10
20
30
40
PEAK LOAD (N) Fig. 6. Peak load to failure in newtons for each technique. Error bars signify standard error.
was used to make individual comparisons between two techniques. Regression analysis was used to assess the relationship of stiffness, peak load, and energy to failure with articular surface percentage and finger size.
Results No differences were evident between technique groups in terms of dorsal fragment size, finger size, or digit. Dorsal fragment size, expressed as a percentage of the articular surface, measured 49% for KW digits, 43% for TBS digits, 41% for TBW digits, and 39% for F8W digits (ANOVA p = 0.551). Finger size was greatest for KW-fixed digital specimens, followed by those fixed with F8W, TBW, and TBS, respectively (ANOVA p = 0.823). An even distribution of digits among technique groups was ensured by the random block experimental design. Technical complications. Technical complications were frequent with both the KW and the TBW tech-
20
40
60
80
100
PERCENT FAILURE Fig. 8. Fraction of specimens (%) that failed irreversibly by residual loss of reduction with the DIP joint replaced in full extension, by implant breakage, or by tears in the tendon insertion.
niques. The only two irreversible errors affecting the final fixation occurred in these two groups. The first was dorsal fragmentation, which occurred during placement of K-wires in one finger. The second occurred when one limb of a TBW was placed just at the lateral border of the dorsal fragment, leaving the dorsal fragment held in place by only one secure strand of the wire. Major difficulties consistently encountered with the KW technique included skiving off of the dorsal fragment, pinning in malreduction, and slippage of the dorsal fragment along the K-wire after pinning. Two minor problems consistently encountered during TB W placement included twisting of the wire and difficulty in passing the wire beneath the tendon-bone axilla. A 21gauge needle was found to be of assistance in passing the wire under the tendon in both the TBW and F8W techniques. During tightening of one TBW, the wire broke but was easily replaced.
Vol. 18A, No. 4 July 1993
Only minor difficulties were encountered with the F8W and TBS methods. These problems included the increased degree of stripping necessary for placement of the transverse drill hole and passage of wire beneath the tendon-bone axilla for the F8W technique. One wire breakage also occurred with the FSW technique, although-this was easily rectified. For the TBS method, the only consistent minor difficulty was in achieving a tight palmar knot. One suture broke but was easily replaced. Overall, 10% of each of the KW and TBW groups were affected by irreversible errors that compromised the ultimate fixation. None of the F8W-or TBS-fixed fingers were so affected. Subjective operator ease was nearly equal for the latter two techniques. The KW technique was thought to be by far the most technically difficult procedure. Biomecbanical testing. Overall energy to failure for all 40 fingers averaged 195.4 N-mm with a standard deviation (SD) of 160.2 (range, 14.2 to 585.3). Overall peak load averaged 28.8 N, but SD was 20.5 N (range, 2.6 to 74.8 N). Overall stiffness averaged 2.46 N/mm with an SD of 2.21 (range, 0.26 to 12.61). Energy absorbed to failure was significantly greater for the FSW and TBS techniques than for the KW technique (p < 0.05) (Fig. 5). Biomechanical testing yielded no statistically significant differences by technique for either peak load (ANOVA p = 0.65) or stiffness (ANOVA p = 0.68). A trend was noted toward greatest peak loads to failure for the TBS method. The wire techniques produced intermediate peak loads, and the KW technique produced the weakest fixation (Fig. 6). A trend toward greatest stiffness for the KW technique was also observed. The wire techniques were intermediate in stiffness. The TBS technique appeared to result in the least stiffness (Fig. 7). There was no significant relationship between stiffness, peak load, or energy to failure and dorsal fragment size, finger size, or digit (Table I). Maintenance of fracture reduction. The consistent mode of failure for the KW method was always slippage of the dorsal fragment along the shaft of the K-wire, leaving the dorsal fragment suspended in a malreduced position. In no case did the fragment reduce into position on return of the DIP joint to an extended position. For the F8W technique, mode of failure was individual tightening of the two loops of the figure eight. Proximally, the wire tightened like a noose around the tendon insertion. Distally, the wire limbs cut transversely into the dorsal cortex. Failure of the TBW-fixed fractures varied. Proximally, the wire tightened around or avulsed the tendon insertion. Distally, the wire cut into bone in a longi-
Mallet jinger fracture jixation techniques
605
Table I. Relationship of stiffness, peak load, and energy absorbed with fragment size,* finger size,* and particular digit? Stt*ess Fragment
size
Finger size Digit
R = 0.236 (p = 0.142) R = 0.175 @ = 0.280) p = 0.192
Peak load
R = 0.106 @ = 0.516) R = 0.143 @ = 0.378) p = 0.151
Energy absorbed
R = 0.093 (p = 0.569) R = 0.218 @ = 0.176) p = 0.308
*By regression analysis. tBy analysis of variance
tudinal direction. Typically, only one limb of the wire cut into the bone, allowing rotational displacement of the dorsal fragment. Mode of failure for the TBS was less evident than for the other techniques. No suture breakage occurred during testing. No tears occurred in the tendon insertion. No cutting of the suture into bone was seen. Some tightening of the suture on the dorsal and palmar soft tissues was evident with the DIP joint flexed 90 degrees. Irreversible failure was defined as residual loss of reduction with the DIP joint replaced in full extension, as implant breakage, or as tears in the tendon insertion. Simple tightening around the tendon insertion was not viewed as irreducible failure unless tears or avulsion of the tendon occurred. All fractures fixed with K-wires failed irreversibly. Irreversible failure also occurred in 60% of the TBW-fixed fractures, either by marginal fragmentation of the dorsal piece (one), complete tendon avulsion (one), or residual fragment displacement (four); 50% of F8W-fixed fractures failed irreversibly by wire breakage (one), partial tendon avulsion (two), or residual displacement (two). No irreversible failures occurred in the TBS group (p = 0.0011) (Fig. 8). Discussion The role of ORIF in the treatment of mallet finger fractures is admittedly limited. It should be reserved primarily for fractures that exhibit residual subluxation or displacement after reduction in a splint. Even in those situations, some authors suggest that splinting yields adequate results by simply avoiding the complications so commonly associated with the reported techniques of internal fixation of these fractures.’ On the other hand, Stem and Kastrup” have demonstrated that complication rates are technique-dependent. The highest complication rates consistently occur with K-wire fixation. Before this study, there had been no report comparing the technical and biomechanical aspects of methods of mallet finger fracture fixation. Despite this paucity of
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objective laboratory data, there appears to be a move away from ORIF of any mallet finger fractures8 The article to which this move can be traced is that of WehbC and Schneider,7 whose method of internal fixation for comparison with splinting involved K-wires. In large part because of the high complication rate of their Kwire technique, they concluded that ORIF showed no advantage over closed treatment by splinting. In contrast, our experience with internal fixation by a pull-out tension band technique has been favorable. (Damron TA, Engber WD. Surgical treatment of mallet finger fractures by tension band technique. Presented at American Society for Surgery of the Hand Annual Resident’s Conference, Phoenix, Ariz., November 1992.) However, a dichotomy has been observed in complication rates between wire (40%) and suture (11%) fixation. All three mechanical complications occurred in fingers fixed with wire. Our technical and biomechanical observations in this study combined with extrapolation from other related biomechanical testing of digits suggest possible explanations for the aforementioned clinical observations. The frequent complications seen clinically with K-wire fixation are not surprising in view of our results. Kwire fixation in this study exhibited consistent technical difficulties, lacked biomechanical superiority, and routinely led to irreversible fragment displacement during testing. Other biomechanical tests, albeit in proximal phalangeal fracture internal fixation, have shown Kwire fixation to be biomechanically inferior to tension band techniques. 23-24The mode of failure when K-wires are used for proximal phalangeal fixation is identical to that observed in this study-slippage of bone on the smooth pins.24, 25 Our observation of more frequent complications with wire than with suture is also supported by our current findings. The TBW technique was similar to the KW technique in terms of technical difficulty and resulted in a similarly large percentage (60%) of irreversibly failed specimens on testing. Whereas the F8W was not thought to be technically difficult, it also frequently led to irreversible failure (50%). The difference in mode of failure between either of the two wire techniques and the suture method appears to account for the dramatic difference in complications. Failure of the wire techniques was usually associated with the wire cutting into bone or soft tissue. The direction differed, depending on orientation of the wire. Neither cutting into bone nor cutting into soft tissue was observed with the suture technique; none of the suture-fixed fractures failed irreversibly during testing. The mode of failure for the suture technique is still unclear. Aside from excluding suture breakage and the
The Journal of HAND SURGERY
cutting into bone or soft tissue, the detection methods of this study were relatively insensitive. Two distinct circumstances might explain the mechanism of failure. First, tightening of the palmar suture loop on the underlying soft tissues of the finger pulp probably occurred. This was apparent, although impossible to quantitate, in each of the specimens. Similar soft tissue tightening likely occurred around the insertion of the extensor tendon. Second, suture knot slippage might have contributed to failure. Our stress-strain curves derived from the testing of TBS specimens were similar to those of previously reported surgical knots that exhibited more than 2 mm of slippage before breaking.26 Whereas Supramid suture material is superior to even monofilament stainless steel at 3 weeks in viva for tendon repairsz7 its in vitro knot efficiency and slippage rate are at best moderate .26*28The importance of knot slippage in this setting is disputable since the thread ends are cut much longer than 2 mm after multiple throws. Multiple throws significantly diminish knot slippage.26, *‘. 29 Despite any possible combination of tightening and/ or slippage, all TBS-fixed fractures returned to a position of anatomic reduction when the DIP joint was replaced into full extension. Hence, regardless of the mechanism of failure during our testing of the TBS technique, it appears to be of little ultimate importance to the final position of the fragments. Certain weaknesses are inherent in our study design and implementation. The relevance of testing internal fixation methods, which are typically protected initially by transarticular K-wire splintage, has been questioned. However, migration of the splinting K-wire is not an infrequent occurrence and requires removal of the Kwire, which leaves the primary mode of internal fixation unprotected. Rigidity adequate to allow early motion was not achieved by any technique tested. The only documented biomechanical superiority was that of the F8W and TBS methods over the KW technique in terms of energy absorbed to failure. The inability to demonstrate statistically significant differences between techniques in terms of peak load and stiffness was probably related to the wide standard deviations for each technique. Greater numbers of specimens and less variability in finger size might have increased our likelihood of statistically demonstrating any real differences. We believed that the techniques should be applied to the most relevant digits to maximize the applicability of the results. Elimination of the small fingers would have reduced the variability in the size of our tested specimens but would have diminished the applicability of this research to fingers other than the most commonly affected digit.3.8 Thumbs were ex-
Vol. 18A, No. 4 July 1993
eluded for two reasons. First, mallet thumb fractures are reported infrequently.30-M Second, the nature of the thumb distal phalanx and extensor tendon insertion is thought to represent a markedly different anatomic situation compared with the more frequently injured digits. Finally, it is possible that the only true biomechanical differences between the techniques are fatigue properties. Since we examined only failure characteristics, we are not able to contribute any data in that regard. We thank Thomas Cook for biostatistics assistance, Mary Marshall for manuscript preparation, and Amy Pahl and Lynn DeWeese for technical typing. REFERENCES 1. Freeman GE. Treatment of mallet finger. Texas State J Med 1963;59:862-3. 2. Stark HH, Boyes JH, Wilson JN. Mallet finger. J Bone Joint Surg 1967;44A:1061-8. 3. Doyle JR. Extensor tendons-acute injuries. In: Green DP, ed. Operative hand surgery. New York Churchill Livingstone, 1984:2066-9. 4. Lange RI-I, Engber WD. Hyperextension mallet finger. Orthopedics 1983;6:1426-31. 5. Groebli Y, Riedo L, Della Santa D, Marti MC. Mallet fractures. Ann Chir Main 1987;6:98-108. 6. Niechajev IA. Conservative and operative treatment of chronic mallet finger. Plast Reconstr Surg 1985;76: 580-5. 7. WehbC MA, Schneider LH. Mallet fractures. J Bone Joint Surg 1984;66A:658-9. 8. Green DP, Rowland SA. Fractures and dislocations in the hand. In: Rockwood CA, Green DP, Bucholz RW, eds. Fractures in adults. Philadelphia: JB Lippincott, 1991:452-3. 9. Kaplan EB. Mallet or baseball finger. Surgery 1940;7:784-91. 10. Kaplan EB. Anatomy, injuries, and treatment of the extensor apparatus of the hand and the digits. Clin Grthop 1959;13:24-40. 11. McFarlane RM, Hampole MK. Treatment of extensor tendon injuries of the hand. Can J Surg 1973;16:366-75. 12. McCue FC, Abbott JL. The treatment of mallet finger and boutonniere deformities. Va Med Monthly 1967; 94:623-g. 13. Casscells SW, Strange TB. Intramedullary wire fixation of mallet finger. J Bone Joint Surg 1957;39A:521-6. 14. Hillman FE. New technique for treatment of mallet fingers and fractures of the distal phalanx. JAMA 1956;161:1135-8. 15. Pratt DR. Internal splint for closed and open treatment of injuries of the extensor tendon at the distal joint of the finger. J Bone Joint Surg 1952;34A:785-8.
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16. Pratt DR, Bunnell S, Howard LD. Mallet finger: classification and methods of treatment. Am J Surg 1957;93:573-9. 17. Hamas RS. Treatment of mallet finger due to intra-articular fracture of the distal phalanx. J HAND SURG 1978;3:361-3. 18. Jupiter JB, Sheppard JE. Tension wire fixation of avulsion fractures in the hand. Clin Orthop 1987;214:11320. 19. Lubahn JD. Mallet finger fractures: a comparison of open and closed technique. J HANDSIJRG 1989;14A:394-6. 20. Weinberg H, Stein HC, Wexler M. A new method of treatment for mallet finger: a preliminary report. Plast Reconstr Surg 1976;58:347-9. 21. Stem PJ, Kastrup JJ. Complications and prognosis of treatment of mallet finger. J HANDSURG 1988;13A:32934. 22. Damron TA, Lange RI-I, Engber WA. Mallet finger: a review and treatment algorithm. Int J Orthop Trauma 1991;1:105-11. 23. Rayhack JM, Belsole RJ, Skelton WH. A strain recording model: analysis of transverse osteotomy fixation in small bones. J HAND SURG 1984;9A:383-7. 24. Black DM, Mann RJ, Constine RM, Daniels AU. The stability of internal fixation in the proximal phalanx. J HANDSURG 1986;11A:672-7. 25. Massengill JB, Alexander H, Langrana N, Mylod A. A phalangeal fracture model: quantitative analysis of rigidity and failure. J HANDSURG 1982;7:264-70. 26. Tera H, Aberg C. Tensile strengths of twelve types of knot employed in surgery, using different suture materials. Acta Chir Stand 1976;142:1-7. 27. Ketchum LD, Martin NL, Kappel DA. Experimental evaluation of factors affecting the strength of tendon repairs. Plast Reconstr Surg 1977;59:708-19. 28. Tera H, Aberg C. Strength of knots in surgery in relation to type of knot, type of suture material and dimension of suture thread. Acta Chir Stand 1977;143:75-83. 29. Holmlund DEW. Knot properties of surgical suture materials: a model study. Acta Chir Stand 1974;140:35562. 30. Din KM, Meggitt BF. Mallet thumb. J Bone Joint Surg 1983;65B:606-7. 31. McGarten GM, Bennett CS, Marshall DR. Treatment of mallet thumb. Aust N Z J Surg 1986;56:285-6. 32. Miura TM, Nakamura R, Torii S. Conservative treatment for a ruptured extensor tendon on the dorsum of the proximal phalanges of the thumb (mallet thumb). J HAND SURG 1986;l lA:229-33. 33. Pate1 MR, Lipson LB, Desai SS. Conservative treatment of mallet thumb. J HANDSURG 1986;11A:45-7. 34. Primiano GA. Conservative treatment of two cases of mallet thumb. J HANDSURG 1986;l lA:233-5.
study was conducted to determine the best fixation technique for mallet finger
among four commonly
biomechanical
used methods.
properties, and maintenance
Considerations
were technical complications,
of reduction. Techniques tested included Kirschner
wire, figure-of-eight wire, tension band wire, and tension band suture. Technical complications were frequent with both the Kirschner wire and tension band wire techniques.
Biomechanical
testing yielded significantly greater energy absorbed to failure and a trend toward greater peak loads to failure for both the figure-of-eight wire and tension band suture techniques. Irreversible loss of reduction during testing occurred in all of the Khschner of the tension band wire-&d No irreversible
wire-fixed
fractures,
fractures, and in 50% of the figure-of-eight wire-fixed
failure occurred in the tension band suture group. (J
HAND
in 60%
fractures.
SURC 1993;18A:
600-7.)
Timothy A. Damron, MD, William D. Engber, MD, Richard H. Lange, MD, Ron McCabe, BS, Leatha A. Damron, BS, Mark Ulm, MS, and Ray Vanderby, PhD, Madison, Wis .
N
o single treatment modality for mallet finger fractures has achieved consistently excellent results in terms of eliminating deformity, stiffness, arthritis, and complications. Treatment options include closed reduction with splinting and numerous techniques for open reduction and internal fixation (ORIF). Early reports support operative repair for dorsal fragments involving more than one third of the articular surface. I-3 However, more recent series suggest that open treatment be reserved for fractures that fail to reduce to a congruent articular arc without subluxation when splinted in extension.4-6 The retrospective review of a large number of mallet finger fractures by WehbC and Schneider’ has been cited
From Division of orthopedics and the Biomechanics Laboratory, Department of Surgery, University of Wisconsin, Madison, Wis. Received for publication 8, 1993.
April 2, 1992; accepted in revised form Jan.
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: William D. Engber, MD, G51322 Clinical Science Center, Division of Chthopedics, University of Wisconsin, 600 Highland Ave., Madison, WI 53792. 311146261
600
THE JOURNAL OF HAND SURGERY
as support for closed treatment of all such injuries, even those associated with subluxation or incongruency in the splint.s At final follow-up, residual pain, dorsal prominence, extensor lag, and degenerative changes were common problems .’ Their preference for splinting appears to be based more on their poor results with operative treatment than on excellent results with nonoperative treatment.’ In our experience, unreduced palmar subluxation is associated with poor outcomes4 Techniques for ORIF of mallet finger fractures have involved fragment fixation with suture, wire, or pins and/ or transarticular pins. ‘-‘a9-2o Reported complications include infection, nail deformity, joint incongruities, fixation/ hardware failure, and secondary deformities .*l In their clinical review of treatment complications, Stem and Kastrup” suggested that complication rates differ significantly between ORIF techniques. The composite of Kirschner (K-) wire fragment fixation and transarticular pinning, exactly the technique used by Wehbe and Schneider,’ was associated with the highest surgical complication rate. Pull-out wires with transarticular pin fixation yielded the lowest complication rate in the series reported by Stem and Kastrup . Despite the abundance of clinical studies, there have previously been no laboratory evaluations of mallet fin-
Vol. 18A, No. 4 July 1993
Mallet finger fracture @cation techniques
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ger fracture fixation techniques. The purpose of this study was to determine the best technique among four commonly used methods. Fixation variables studied included the stability of fixation maintenance after loading and the frequency of technical problems associated with each technique. Materials and methods Ten fresh frozen hands were acquired from donors 47 to 70 years old with no history of chemotherapy, local radiotherapy, or prolonged steroid usage. Whole hands were procured within 12 hours after death and frozen at - 70” C. The hands were individually thawed to allow fracture simulation and fixation. The base of the distal phalanx was exposed on the index, long, ring, and small fingers; thumbs were not used. The nail was removed to avoid interference with the osteotomy cut. Reproducible fracture simulation was done by making an oblique dorsal cut at the base of the distal phalanx over a K-wire 0.027 inch in diameter by means of a 0.03 cm thick blade on a microsagittal saw under fluoroscopic control (Fig. 1, A). The osteotomy created a dorsal fragment involving an average of 45% (range, 29% to 60%) of the attic&u surface as measured on a true lateral fluoroscopic print of the cut digit. The extensor tendon insertion on this dorsal fragment was preserved. Fluorographic prints were made of each cut to document the size of the dorsal fragment (Fig. 1, B). Techniques were assigned among fingers in a randomized block fashion. Techniques tested included fixation with K-wires (KW),’ figure-of-eight wire (F8W),” tension band wire (TBW),** and tension band suture (TBS).** Only one technique was performed on each digit. All of the procedures were performed by one surgeon (T.A.D.). The KW technique was used in the fashion reported by WehbC and Schneider, directing two 0.035inch K-wires from dorsally and proximally through the dorsal fragment in a palmar and distal direction into the major portion of the distal phalanx.’ Fluoroscopic control was used to guide reduction and fixation. The wires were cut and left unbent after placement. The F8W technique followed the description by Jupiter and Sheppard. ‘* A 28-gauge stainless steel wire was directed beneath the tendon insertion, over the dorsal fragment, and through a transverse hole in the dorsal aspect of the major portion of the distal phalanx just distal to the osteotomy cut. The hole was created with a 21-gauge needle through which the wire was passed. The wire was tightened over the dorsal surface in a
Fig. 1. Technique for mallet fracture simulation and fixation by TBS. A, Pluorographic print negative lateral view of the DIP joint shows K-wire guide positioned in distal phalanx from dorsal-distal to an intra-articular position to serve as a guide for the cutting blade. B, Dorsal articular fragment of same specimen has been created by cutting along the K-wire guide with a microsagittal saw blade. C, Reduction and fixation of same specimen has been achieved with the TBS technique.
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Fig. 2. Technique for mallet fracture simulation and fixation by F8W. A, K-wire guide is in position, B, Dorsal articular fragment has been created. C, Reduction and fixation have been achieved with the F8W technique.
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Fig. 3. Detailed operative technique for TBS and TBW. A, Placement of suture anterior to insertion of extensor with strands directed dorsally over fragment. B, Keith needles used to pass suture ends through distal phalanx. C, Dorsal view of reduced fracture with sutures pulled taut. D, Preparation for tying suture through button on palmar aspect. Clinically, a TeIfa pad is used beneath the button to protect the skin.
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Fig. 4. Testing apparatus. Amputated specimen is held in position by middle phalangeal intramedullary screw. Extensor tendon is pulled taut around capstan device. Loading device connected to ram on Bionix MTS 858 servohydraulic load frame is lowered into contact with distal phalanx just distal to osteotomy site. Central portion of loading device is scalloped (not shown) to avoid contact with middle phalanx during testing excursion. figure-of-eight
fashion
with a single limb twist (Fig.
2). Both the TBW and TBS procedures were performed in identical fashion, with the use of 28-gauge stainless steel wire for TBW and 2-O Supramid sutures (S. Jackson Inc., Alexandria, Va.) for TBS (Fig. 3).22 The tension band material was passed beneath the extensor tendon in the axilla between tendon insertion and bone of the dorsal fragment. The strands were then directed dorsally over the dorsal fragment through the dorsal epitenon. Two drill holes were created for these two strands, beginning just distal to the osteotomy site and directed palmarly and distally through the palmar skin of the finger. A 21-gauge needle was used to create the drill hole for passage of the wire, and a Keith needle was used for passage of the suture. The limbs were then pulled through and twisted or tied palmarly (Fig. 1, 0. Each specimen was amputated at the proximal interphalangeal joint, maintaining the attached extensor tendon, which was transected at its musculotendinous junction. The proximal intramedullary canal of the middle phalanx was drilled with a 2.0 mm drill and tapped with a 2.7 mm tap. The length, width, and depth of the specimens were measured with calipers. All biomechanical testing was done on a single day.
The middle phalanx was mounted rigidly to the testing device with a 2.7 mm cortical screw (Fig. 4). The extensor tendon was wrapped around a roughened capstan device that was tightened with a torque wrench to 12 inch-ounces to keep the distal interphalangeal joint (DIP) fully extended. The Bionix MTS 858 servohydraulic load frame (MTS, Minneapolis, Minn.) was then used to apply a flexion load just distal to the osteotomy over a 3 cm ramp excursion that lasted 2 seconds. Markings on the extensor tendon did not move relative to the grips during the testing, which confirmed the absence of loosening of the tendon on the capstan device. The end point of flexion was displacement at the osteotomy site in 90 degrees of flexion. Each finger was removed from the testing device and inspected closely for mode of failure. The extensor tendon was then pulled into full extension again, and fluorographic prints were obtained to document the extent of residual displacement. A load-deformation curve was plotted for each digit, from which stiffness, peak load, and energy to failure were derived. Statistical analysis was performed under the guidance of a statistician with the use of Statistical Analysis System (SAS) software. Analysis of variance (ANOVA) was performed to identify differences in numerical variables between technique groups. Fisher’s Exact Test
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TBW TBS
KW
* P < 0.05 0 0
loo
for
3
4
STIFFNESS (N/mm)
ENERGY ABSORBED (N-mm) Fig. 5. Energy absorbed to failure in newton-millimeters each technique. Error bars signify standard error.
2
1
300
200
Fig. 7. Stiffness in newtons per millimeter for each technique. Error bars signify standard error.
TBW TBS TBS
* P = 0.0011
Q c
FSW
DirpsocslRnr orTerrden Tear
c
V
A
KW KW
0 0
10
20
30
40
PEAK LOAD (N) Fig. 6. Peak load to failure in newtons for each technique. Error bars signify standard error.
was used to make individual comparisons between two techniques. Regression analysis was used to assess the relationship of stiffness, peak load, and energy to failure with articular surface percentage and finger size.
Results No differences were evident between technique groups in terms of dorsal fragment size, finger size, or digit. Dorsal fragment size, expressed as a percentage of the articular surface, measured 49% for KW digits, 43% for TBS digits, 41% for TBW digits, and 39% for F8W digits (ANOVA p = 0.551). Finger size was greatest for KW-fixed digital specimens, followed by those fixed with F8W, TBW, and TBS, respectively (ANOVA p = 0.823). An even distribution of digits among technique groups was ensured by the random block experimental design. Technical complications. Technical complications were frequent with both the KW and the TBW tech-
20
40
60
80
100
PERCENT FAILURE Fig. 8. Fraction of specimens (%) that failed irreversibly by residual loss of reduction with the DIP joint replaced in full extension, by implant breakage, or by tears in the tendon insertion.
niques. The only two irreversible errors affecting the final fixation occurred in these two groups. The first was dorsal fragmentation, which occurred during placement of K-wires in one finger. The second occurred when one limb of a TBW was placed just at the lateral border of the dorsal fragment, leaving the dorsal fragment held in place by only one secure strand of the wire. Major difficulties consistently encountered with the KW technique included skiving off of the dorsal fragment, pinning in malreduction, and slippage of the dorsal fragment along the K-wire after pinning. Two minor problems consistently encountered during TB W placement included twisting of the wire and difficulty in passing the wire beneath the tendon-bone axilla. A 21gauge needle was found to be of assistance in passing the wire under the tendon in both the TBW and F8W techniques. During tightening of one TBW, the wire broke but was easily replaced.
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Only minor difficulties were encountered with the F8W and TBS methods. These problems included the increased degree of stripping necessary for placement of the transverse drill hole and passage of wire beneath the tendon-bone axilla for the F8W technique. One wire breakage also occurred with the FSW technique, although-this was easily rectified. For the TBS method, the only consistent minor difficulty was in achieving a tight palmar knot. One suture broke but was easily replaced. Overall, 10% of each of the KW and TBW groups were affected by irreversible errors that compromised the ultimate fixation. None of the F8W-or TBS-fixed fingers were so affected. Subjective operator ease was nearly equal for the latter two techniques. The KW technique was thought to be by far the most technically difficult procedure. Biomecbanical testing. Overall energy to failure for all 40 fingers averaged 195.4 N-mm with a standard deviation (SD) of 160.2 (range, 14.2 to 585.3). Overall peak load averaged 28.8 N, but SD was 20.5 N (range, 2.6 to 74.8 N). Overall stiffness averaged 2.46 N/mm with an SD of 2.21 (range, 0.26 to 12.61). Energy absorbed to failure was significantly greater for the FSW and TBS techniques than for the KW technique (p < 0.05) (Fig. 5). Biomechanical testing yielded no statistically significant differences by technique for either peak load (ANOVA p = 0.65) or stiffness (ANOVA p = 0.68). A trend was noted toward greatest peak loads to failure for the TBS method. The wire techniques produced intermediate peak loads, and the KW technique produced the weakest fixation (Fig. 6). A trend toward greatest stiffness for the KW technique was also observed. The wire techniques were intermediate in stiffness. The TBS technique appeared to result in the least stiffness (Fig. 7). There was no significant relationship between stiffness, peak load, or energy to failure and dorsal fragment size, finger size, or digit (Table I). Maintenance of fracture reduction. The consistent mode of failure for the KW method was always slippage of the dorsal fragment along the shaft of the K-wire, leaving the dorsal fragment suspended in a malreduced position. In no case did the fragment reduce into position on return of the DIP joint to an extended position. For the F8W technique, mode of failure was individual tightening of the two loops of the figure eight. Proximally, the wire tightened like a noose around the tendon insertion. Distally, the wire limbs cut transversely into the dorsal cortex. Failure of the TBW-fixed fractures varied. Proximally, the wire tightened around or avulsed the tendon insertion. Distally, the wire cut into bone in a longi-
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Table I. Relationship of stiffness, peak load, and energy absorbed with fragment size,* finger size,* and particular digit? Stt*ess Fragment
size
Finger size Digit
R = 0.236 (p = 0.142) R = 0.175 @ = 0.280) p = 0.192
Peak load
R = 0.106 @ = 0.516) R = 0.143 @ = 0.378) p = 0.151
Energy absorbed
R = 0.093 (p = 0.569) R = 0.218 @ = 0.176) p = 0.308
*By regression analysis. tBy analysis of variance
tudinal direction. Typically, only one limb of the wire cut into the bone, allowing rotational displacement of the dorsal fragment. Mode of failure for the TBS was less evident than for the other techniques. No suture breakage occurred during testing. No tears occurred in the tendon insertion. No cutting of the suture into bone was seen. Some tightening of the suture on the dorsal and palmar soft tissues was evident with the DIP joint flexed 90 degrees. Irreversible failure was defined as residual loss of reduction with the DIP joint replaced in full extension, as implant breakage, or as tears in the tendon insertion. Simple tightening around the tendon insertion was not viewed as irreducible failure unless tears or avulsion of the tendon occurred. All fractures fixed with K-wires failed irreversibly. Irreversible failure also occurred in 60% of the TBW-fixed fractures, either by marginal fragmentation of the dorsal piece (one), complete tendon avulsion (one), or residual fragment displacement (four); 50% of F8W-fixed fractures failed irreversibly by wire breakage (one), partial tendon avulsion (two), or residual displacement (two). No irreversible failures occurred in the TBS group (p = 0.0011) (Fig. 8). Discussion The role of ORIF in the treatment of mallet finger fractures is admittedly limited. It should be reserved primarily for fractures that exhibit residual subluxation or displacement after reduction in a splint. Even in those situations, some authors suggest that splinting yields adequate results by simply avoiding the complications so commonly associated with the reported techniques of internal fixation of these fractures.’ On the other hand, Stem and Kastrup” have demonstrated that complication rates are technique-dependent. The highest complication rates consistently occur with K-wire fixation. Before this study, there had been no report comparing the technical and biomechanical aspects of methods of mallet finger fracture fixation. Despite this paucity of
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objective laboratory data, there appears to be a move away from ORIF of any mallet finger fractures8 The article to which this move can be traced is that of WehbC and Schneider,7 whose method of internal fixation for comparison with splinting involved K-wires. In large part because of the high complication rate of their Kwire technique, they concluded that ORIF showed no advantage over closed treatment by splinting. In contrast, our experience with internal fixation by a pull-out tension band technique has been favorable. (Damron TA, Engber WD. Surgical treatment of mallet finger fractures by tension band technique. Presented at American Society for Surgery of the Hand Annual Resident’s Conference, Phoenix, Ariz., November 1992.) However, a dichotomy has been observed in complication rates between wire (40%) and suture (11%) fixation. All three mechanical complications occurred in fingers fixed with wire. Our technical and biomechanical observations in this study combined with extrapolation from other related biomechanical testing of digits suggest possible explanations for the aforementioned clinical observations. The frequent complications seen clinically with K-wire fixation are not surprising in view of our results. Kwire fixation in this study exhibited consistent technical difficulties, lacked biomechanical superiority, and routinely led to irreversible fragment displacement during testing. Other biomechanical tests, albeit in proximal phalangeal fracture internal fixation, have shown Kwire fixation to be biomechanically inferior to tension band techniques. 23-24The mode of failure when K-wires are used for proximal phalangeal fixation is identical to that observed in this study-slippage of bone on the smooth pins.24, 25 Our observation of more frequent complications with wire than with suture is also supported by our current findings. The TBW technique was similar to the KW technique in terms of technical difficulty and resulted in a similarly large percentage (60%) of irreversibly failed specimens on testing. Whereas the F8W was not thought to be technically difficult, it also frequently led to irreversible failure (50%). The difference in mode of failure between either of the two wire techniques and the suture method appears to account for the dramatic difference in complications. Failure of the wire techniques was usually associated with the wire cutting into bone or soft tissue. The direction differed, depending on orientation of the wire. Neither cutting into bone nor cutting into soft tissue was observed with the suture technique; none of the suture-fixed fractures failed irreversibly during testing. The mode of failure for the suture technique is still unclear. Aside from excluding suture breakage and the
The Journal of HAND SURGERY
cutting into bone or soft tissue, the detection methods of this study were relatively insensitive. Two distinct circumstances might explain the mechanism of failure. First, tightening of the palmar suture loop on the underlying soft tissues of the finger pulp probably occurred. This was apparent, although impossible to quantitate, in each of the specimens. Similar soft tissue tightening likely occurred around the insertion of the extensor tendon. Second, suture knot slippage might have contributed to failure. Our stress-strain curves derived from the testing of TBS specimens were similar to those of previously reported surgical knots that exhibited more than 2 mm of slippage before breaking.26 Whereas Supramid suture material is superior to even monofilament stainless steel at 3 weeks in viva for tendon repairsz7 its in vitro knot efficiency and slippage rate are at best moderate .26*28The importance of knot slippage in this setting is disputable since the thread ends are cut much longer than 2 mm after multiple throws. Multiple throws significantly diminish knot slippage.26, *‘. 29 Despite any possible combination of tightening and/ or slippage, all TBS-fixed fractures returned to a position of anatomic reduction when the DIP joint was replaced into full extension. Hence, regardless of the mechanism of failure during our testing of the TBS technique, it appears to be of little ultimate importance to the final position of the fragments. Certain weaknesses are inherent in our study design and implementation. The relevance of testing internal fixation methods, which are typically protected initially by transarticular K-wire splintage, has been questioned. However, migration of the splinting K-wire is not an infrequent occurrence and requires removal of the Kwire, which leaves the primary mode of internal fixation unprotected. Rigidity adequate to allow early motion was not achieved by any technique tested. The only documented biomechanical superiority was that of the F8W and TBS methods over the KW technique in terms of energy absorbed to failure. The inability to demonstrate statistically significant differences between techniques in terms of peak load and stiffness was probably related to the wide standard deviations for each technique. Greater numbers of specimens and less variability in finger size might have increased our likelihood of statistically demonstrating any real differences. We believed that the techniques should be applied to the most relevant digits to maximize the applicability of the results. Elimination of the small fingers would have reduced the variability in the size of our tested specimens but would have diminished the applicability of this research to fingers other than the most commonly affected digit.3.8 Thumbs were ex-
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eluded for two reasons. First, mallet thumb fractures are reported infrequently.30-M Second, the nature of the thumb distal phalanx and extensor tendon insertion is thought to represent a markedly different anatomic situation compared with the more frequently injured digits. Finally, it is possible that the only true biomechanical differences between the techniques are fatigue properties. Since we examined only failure characteristics, we are not able to contribute any data in that regard. We thank Thomas Cook for biostatistics assistance, Mary Marshall for manuscript preparation, and Amy Pahl and Lynn DeWeese for technical typing. REFERENCES 1. Freeman GE. Treatment of mallet finger. Texas State J Med 1963;59:862-3. 2. Stark HH, Boyes JH, Wilson JN. Mallet finger. J Bone Joint Surg 1967;44A:1061-8. 3. Doyle JR. Extensor tendons-acute injuries. In: Green DP, ed. Operative hand surgery. New York Churchill Livingstone, 1984:2066-9. 4. Lange RI-I, Engber WD. Hyperextension mallet finger. Orthopedics 1983;6:1426-31. 5. Groebli Y, Riedo L, Della Santa D, Marti MC. Mallet fractures. Ann Chir Main 1987;6:98-108. 6. Niechajev IA. Conservative and operative treatment of chronic mallet finger. Plast Reconstr Surg 1985;76: 580-5. 7. WehbC MA, Schneider LH. Mallet fractures. J Bone Joint Surg 1984;66A:658-9. 8. Green DP, Rowland SA. Fractures and dislocations in the hand. In: Rockwood CA, Green DP, Bucholz RW, eds. Fractures in adults. Philadelphia: JB Lippincott, 1991:452-3. 9. Kaplan EB. Mallet or baseball finger. Surgery 1940;7:784-91. 10. Kaplan EB. Anatomy, injuries, and treatment of the extensor apparatus of the hand and the digits. Clin Grthop 1959;13:24-40. 11. McFarlane RM, Hampole MK. Treatment of extensor tendon injuries of the hand. Can J Surg 1973;16:366-75. 12. McCue FC, Abbott JL. The treatment of mallet finger and boutonniere deformities. Va Med Monthly 1967; 94:623-g. 13. Casscells SW, Strange TB. Intramedullary wire fixation of mallet finger. J Bone Joint Surg 1957;39A:521-6. 14. Hillman FE. New technique for treatment of mallet fingers and fractures of the distal phalanx. JAMA 1956;161:1135-8. 15. Pratt DR. Internal splint for closed and open treatment of injuries of the extensor tendon at the distal joint of the finger. J Bone Joint Surg 1952;34A:785-8.
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16. Pratt DR, Bunnell S, Howard LD. Mallet finger: classification and methods of treatment. Am J Surg 1957;93:573-9. 17. Hamas RS. Treatment of mallet finger due to intra-articular fracture of the distal phalanx. J HAND SURG 1978;3:361-3. 18. Jupiter JB, Sheppard JE. Tension wire fixation of avulsion fractures in the hand. Clin Orthop 1987;214:11320. 19. Lubahn JD. Mallet finger fractures: a comparison of open and closed technique. J HANDSIJRG 1989;14A:394-6. 20. Weinberg H, Stein HC, Wexler M. A new method of treatment for mallet finger: a preliminary report. Plast Reconstr Surg 1976;58:347-9. 21. Stem PJ, Kastrup JJ. Complications and prognosis of treatment of mallet finger. J HANDSURG 1988;13A:32934. 22. Damron TA, Lange RI-I, Engber WA. Mallet finger: a review and treatment algorithm. Int J Orthop Trauma 1991;1:105-11. 23. Rayhack JM, Belsole RJ, Skelton WH. A strain recording model: analysis of transverse osteotomy fixation in small bones. J HAND SURG 1984;9A:383-7. 24. Black DM, Mann RJ, Constine RM, Daniels AU. The stability of internal fixation in the proximal phalanx. J HANDSURG 1986;11A:672-7. 25. Massengill JB, Alexander H, Langrana N, Mylod A. A phalangeal fracture model: quantitative analysis of rigidity and failure. J HANDSURG 1982;7:264-70. 26. Tera H, Aberg C. Tensile strengths of twelve types of knot employed in surgery, using different suture materials. Acta Chir Stand 1976;142:1-7. 27. Ketchum LD, Martin NL, Kappel DA. Experimental evaluation of factors affecting the strength of tendon repairs. Plast Reconstr Surg 1977;59:708-19. 28. Tera H, Aberg C. Strength of knots in surgery in relation to type of knot, type of suture material and dimension of suture thread. Acta Chir Stand 1977;143:75-83. 29. Holmlund DEW. Knot properties of surgical suture materials: a model study. Acta Chir Stand 1974;140:35562. 30. Din KM, Meggitt BF. Mallet thumb. J Bone Joint Surg 1983;65B:606-7. 31. McGarten GM, Bennett CS, Marshall DR. Treatment of mallet thumb. Aust N Z J Surg 1986;56:285-6. 32. Miura TM, Nakamura R, Torii S. Conservative treatment for a ruptured extensor tendon on the dorsum of the proximal phalanges of the thumb (mallet thumb). J HAND SURG 1986;l lA:229-33. 33. Pate1 MR, Lipson LB, Desai SS. Conservative treatment of mallet thumb. J HANDSURG 1986;11A:45-7. 34. Primiano GA. Conservative treatment of two cases of mallet thumb. J HANDSURG 1986;l lA:233-5.